About

Dr. Paul Christo is a leading pain specialist and author of Aches and Gains, A Comprehensive Guide to Overcoming Your Pain. He serves as the Chief and Associate Professor of the Division of Pain Medicine at the Johns Hopkins University School of Medicine. Dr. Christo has served as Director of the Multidisciplinary Pain Fellowship Program for eight years and the Blaustein Pain Treatment Center for five years at the Johns Hopkins Hospital. He is an invited lecturer both nationally and internationally, and serves on four journal editorial boards. He has published more than 100 articles and book chapters, co-edited five textbooks on pain, and actively teaches medical students, residents, and pain fellows. His clinical practice involves treating a wide variety of patients with chronic pain, including conditions such as low back and neck pain, disc herniation, spinal stenosis, headache, neuropathic pain, cancer pain, musculoskeletal pain, persistent postoperative pain, craniofacial pain, and pelvic pain. A subspecialty focus is neurogenic thoracic outlet syndrome (NTOS), which involves nerve compression in the neck causing pain and sensory symptoms, often managed with anesthetic blocks or botulinum toxin injections. Dr. Christo has also studied the beneficial effects of auricular acupressure for musculoskeletal pain relief. He performs numerous pain-relieving procedures, including nerve blocks, joint injections, radiofrequency procedures, neuromodulation, and minimally invasive surgeries. Additionally, he hosts the nationally syndicated radio talk show Aches and Gains®, which provides education and hope for those suffering from pain and medical illnesses. His contributions to public education and pain medicine have earned him several awards, including the John and Emma Bonica Public Service Award and the Patient Advocacy Award from the American Academy of Pain Medicine. Dr. Christo holds an M.B.A. from the Johns Hopkins Carey Business School in Health Care Management and has served on various advisory boards and professional organizations dedicated to pain management and education.

Research topics

• Biophysics
• Biology
• Cell biology
• Biochemistry
• Chemistry

Selected publications

• Desktop Learning Module Heat Exchanger Performance

  2025-02-18 · 4 citations

  articleOpen access1st authorCorresponding

  Researchers at Washington State University have developed miniaturized hands-on learning stations or Desktop Learning Modules (DLM) to help demonstrate most basic fluid and heat transfer concepts in the classroom.Low-cost, 1 ft 3 modules have been developed with interchangeable cartridges for dye injection into a flow stream; flow measurement with venturi, orifice and pitot tube meters; shell-and-tube, extended area and double pipe heat exchange; and packed bed and fluidized bed performance.The DLMs are effective learning tools, but are they useful in collecting laboratory data?An experimental study was performed to determine the duty of the DLM shell-and-tube heat exchanger, and then to compare the results to theoretical predictions.Although a few minor modifications of the apparatus were necessary in order to obtain accurate data, experimental heat transfer rates on the tube side (539-831 W) were within 15-20% of theoretical predictions.Similarly, experimental heat transfer rates on the shell side (681-1,068 W) were within 1-11% of theoretical.

  PublisherOA PDFDOI

• Author Correction: A microfluidic assay for the quantification of the metastatic propensity of breast cancer specimens

  Nature Biomedical Engineering · 2025-02-05

  erratumOpen access
  PublisherOA PDFDOI

• Long-term maintenance of patient-specific characteristics in tumoroids from six cancer indications

  Scientific Reports · 2025-01-31 · 12 citations

  articleOpen access1st authorCorresponding

  Tumoroids, sometimes referred to as cancer organoids, are patient-derived cancer cells grown as 3D, self-organized multicellular structures that maintain key characteristics (e.g., genotype, gene expression levels) of the tumor from which they originated. These models have emerged as valuable tools for studying tumor biology, cytotoxicity, and response of patient-derived cells to cancer therapies. However, the establishment and maintenance of tumoroids has historically been challenging, labor intensive, and highly variable from lab to lab, hindering their widespread use. Here, we characterize the establishment and/or expansion of colorectal, lung, head and neck, breast, pancreas, and endometrial tumoroids using the standardized, serum-free Gibco OncoPro Tumoroid Culture Medium. Newly derived tumoroid lines (n = 20) were analyzed by targeted genomic profiling and RNA sequencing and were representative of tumor tissue samples. Tumoroid lines were stable for over 250 days in culture and freeze-thaw competent. Previously established tumoroid lines were also transitioned to OncoPro medium and exhibited, on average, similar growth rates and conserved donor-specific characteristics when compared to original media systems. Additionally, OncoPro medium was compatible with both embedded culture in extracellular matrix and growth in a suspension format for facile culture and scale up. An example application of these models for assessing the cytotoxicity of a natural killer cell line and primary natural killer cells over time and at various doses demonstrated the compatibility of these models with assays used in compound and cell therapy development. We anticipate that the standardization and versatility of this approach will have important benefits for basic cancer research, drug discovery, and personalized medicine and help make tumoroid models more accessible to the cancer research community.

  PublisherDOI

• Abstract 3985: Optimizing co-culture of tumoroid and immune cells for recapitulation of the tumor microenvironment

  Cancer Research · 2025-04-21

  article

  Abstract Immunotherapies for solid cancer treatment aim to potentiate immune cell recognition of cancer cells within the tumor microenvironment or recruit peripheral immune cells (native or engineered) to the tumor. Patient-derived tumoroids, or cancer organoids, are multicellular structures that closely mimic the architecture and genetic and transcriptomic landscape of tumors. When co-cultured with immune cells, these models enable a more comprehensive investigation of the tumor-immune microenvironment than traditional cancer cell lines. However, culture conditions to prolong survival of both epithelial cancer cells and immune cells remain poorly defined. Here, we explored methods to supplement Gibco™ OncoPro™ Tumoroid Culture Medium to promote immune cell survival for better recapitulation of the tumor microenvironment. In initial experiments, healthy donor PBMCs were thawed and cultured in suspension in OncoPro medium for 5 days. Total viable cells were counted at the end of the culture period and revealed loss of 80±2% of the cells initially present. Similarly, RNA sequencing comparing freshly dissociated colorectal and endometrial tumors with cells cultured for 7 days in OncoPro medium indicated downregulation of genes related to immune cell signaling pathways, and flow cytometry of tumoroid models showed loss of immune cell populations over time compared to the initial material. Therefore, designed experiments were used to screen and optimize cytokine cocktails that maximized PBMC survival while minimizing the change in the percentage of monocytes, B cells, NK cells, helper T cells, and cytotoxic T cells between the original (day 0) donor material and in vitro PBMC cultures. Cytokine addition led to an increase in PBMC cell number after 5 days in culture of 2.2±0.8x compared to culture in non-supplemented OncoPro medium across three independent donors, with <10% change in the relative proportion of cells in the immune compartments examined over the culture period. Follow up experiments are focused on determining conditions that support the survival of immune cells present in cryopreserved dissociated tumor cell (DTC) samples using cytokines identified during PBMC screening experiments. In preliminary work, the addition of cytokines to potentiate immune cell survival did not negatively affect the culture of epithelial tumoroid cells. Co-culture of immune cells with tumoroids will facilitate the examination of immune checkpoint inhibitors and other immunotherapy strategies in vitro to enable higher throughput and more controlled screening of immunotherapy candidates. We envision that this approach will provide critical insights into the mechanisms of immune evasion and resistance and potentially lead to more effective treatment options for cancer patients. Citation Format: Shyanne Salen, Sydney Hawkins, Sylvia Beam, Colin D. Paul, Chris Yankaskas, Pradip Shahi Thakuri, Matt Dallas, David Kuninger. Optimizing co-culture of tumoroid and immune cells for recapitulation of the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3985.

  PublisherDOI

• Abstract B017: An integrated workflow for multiomic characterization and functional precision medicine testing of solid tumor samples

  Cancer Research · 2025-03-11

  article1st authorCorresponding

  Abstract The development of tumoroid (or cancer organoid) technology has enabled the in vitro culture of patient-derived cancer cells that retain key morphological, mutational, and transcriptomic characteristics of patient tumors. In a number of studies, the response of tumoroids to therapies has mirrored that seen in the patients from which the tumoroids were derived. As a result, there is increasing interest in the use of tumoroids in functional precision oncology, in which an individual patient’s cancer cells are used as ex vivo tumor avatars and tested for response to a range of various potential treatments to aid in therapy selection. Here, we explored a workflow to integrate genomic sequencing with functional drug sensitivity testing for precision medicine applications. Excess FFPE tissue from 6 colorectal cancer donors was processed to generate H&E slides and unstained sections. Slides (2 x 10 µm sections per donor) were digested, and RNA and DNA were isolated using an automated nucleic acid purification system. The output samples were analyzed on the Genexus™ Integrated Sequencer for targeted detection of SNVs, CNVs, gene fusions, and indels for each sample using the Oncomine™ Comprehensive Assay v3. Purified RNA was also utilized for bulk RNA sequencing to generate transcriptomic profiles for each donor. In parallel, viably cryopreserved dissociated tumor cells (DTCs) were thawed and plated in Gibco™ OncoPro™ Tumoroid Culture Medium, a commercially available, serum-free, and conditioned medium-free system. OncoPro medium was developed and optimized for the culture of patient-derived tumor cells from solid cancers to provide an easy-to-use, reproducible, cGMP manufactured culture system for these samples. Where sample size allowed, RNA was isolated from DTC samples and sequenced to compare transcriptomic results generated from FFPE vs. viably cryopreserved material. Additionally, DTCs were sampled for untargeted proteomic and metabolomic profiling. DTCs were cultured for 3-7 days in OncoPro medium prior to exposure to chemotherapy drugs used in standard-of-care treatment for colorectal cancer, and cell response was quantified. Dissociated tumoroid cells formed tumoroids at high rates in culture, in line with previous studies showing that patient-derived cancer cells across colorectal, endometrial, lung, breast, and head and neck cancers form tumoroids in OncoPro medium in >85% of samples within 7 days of tissue receipt. We observed heterogeneous genomic, proteomic, transcriptomic, and drug response profiles across donors. Current efforts are focused on development of computational methods to tie multiomic characterization with functional response. Overall, this data presents an integrated workflow to combine genomic approaches with functional testing to inform patient care. Citation Format: Colin D Paul, Amber Bullock, Anthony Chatman, Km Shams Ud Doha, Harrison Leong, Sylvia Beam, Chris Yankaskas, Pradip Shahi Thakuri, Matt Dallas, David Kuninger. An integrated workflow for multiomic characterization and functional precision medicine testing of solid tumor samples [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Functional and Genomic Precision Medicine in Cancer: Different Perspectives, Common Goals; 2025 Mar 11-13; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(5 Suppl):Abstract nr B017.

  PublisherDOI

• Abstract 883: Scalable differentiation of cytotoxic natural killer (NK) cells from human pluripotent stem cells

  Cancer Research · 2025-04-21

  article

  Cell therapy is expanding as a treatment for various cancers. FDA-approved autologous therapies, such as chimeric antigen receptor (CAR) T cells and tumor infiltrating lymphocytes (TILs), are used for aggressive or late-stage cancers. However, these therapies face challenges due to lengthy manufacturing times and patient variability. Manufacturing is already a bottleneck, which is expected to worsen as these therapies are tested in earlier cancer stages and become available to more patients. An emerging solution for cancer treatment is the use of natural killer (NK) cells as an "off-the-shelf" therapy. These cells target malignant cells independent of antigens, without needing HLA matching, and have not caused cytokine release syndrome like some T cell therapies. Clinical trials typically administer 5x10^6 to 1x10^8 NK cells per kilogram of body weight per dose. Therefore, developing methods to produce large quantities of functional NK cells is crucial. Current methods, such as sourcing primary cells or differentiating from human pluripotent stem cells (PSCs) in two dimensions (2D), yield variable results, often require co-culture or embryoid body formation, and usually fail to produce enough functional NK cells for therapy. To address these limitations, we developed a scalable 3D PSC culture differentiation protocol to hematopoietic stem cells (iHSCs), a multipotent progenitor cell population, and then to induced natural killer (iNK) cells that primarily uses GMP grade reagents with regulatory documentation. Differentiation occurs in suspension using shake flasks. After 38 days, over 50% of cells are CD56+ CD3-, and can be cryopreserved, thawed, and further expanded. This method, tested in up to 100 mL cultures, produces 5-10x106 CD56+CD3- iNK cells/mL, sufficient to treat one patient at the lower dosing range. Multiple 100 mL cultures can be cultivated in parallel to increase the yield, and future efforts will focus on optimizing the protocol in larger culture volumes. To evaluate iNK cell cytotoxicity, they were co-cultured with three-dimensional (3D) patient-derived cancer organoids, a physiologically relevant in vitro cancer culture that better mimics tumor tissue than traditional 2D cancer cell lines and are harder to kill. iNK cells induced apoptosis in breast, colorectal, and endometrial cancer organoids in a dose-dependent manner. Against the same target colorectal cancer organoids, iNKs were more cytotoxic than the NK-92 cell line at equal doses, and matched primary NK cells at roughly double the dose. In summary, we demonstrate a novel scalable protocol for generating functional iNK cells, showing potency in a cytotoxicity assay with patient-derived cancer organoids, which could be further developed for cell therapy research. Citation Format: Marcus Bunn, Lindsay Bailey Steinitz, Vivek Chandra, Michael Akenhead, Logan Wilson, Erica Heipertz, Chris Yankaskas, Colin Paul, Matt Dallas, Mark Kennedy, David Kuninger. Scalable differentiation of cytotoxic natural killer (NK) cells from human pluripotent stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 883.

  PublisherDOI

• Abstract 5193: Optimization of tumoroid size and payload delivery methods for the engineering of patient-derived tumoroid models

  Cancer Research · 2025-04-21

  article

  Abstract Tumoroids, also known as cancer organoids, are three-dimensional (3D) in vitro cell cultures established from primary tissue samples. These next-generation cancer cell models largely recapitulate the spatial organization, gene expression, and mutational profiles of patient tumors. It may be beneficial to engineer tumoroids to generate reporter lines, model specific mutations involved with tumor progression, or modulate gene expression to help understand the mechanism of action of therapeutics. Here, we explore methods for genetic engineering of tumoroids established and cultured in Gibco™ OncoPro™ Tumoroid Culture Medium to facilitate these studies. We first examined the impact of tumoroid size on transfection efficiency via electroporation with the Neon™ NxT Electroporation System. Colorectal tumoroids were transfected with enhanced green fluorescent protein (eGFP) immediately after dissociation or after 4 or 7 days in culture in OncoPro medium, at which point tumoroid size had reached approximately 400 µm in diameter. Nearly 80% of dissociated tumoroids were successfully transfected, while efficiency dropped to 35-40% when using intact 4- or 7-day old tumoroids. Therefore, dissociated tumoroids were used for further experiments. We then compared lipofection, electroporation, and lentivirus-based transduction in a difficult-to-transfect model, focusing on reporter line generation. While lipofection is easy-to-use and cost effective, delivery of enhanced green fluorescent protein (eGFP) by lipofection led to transfection efficiencies of only 15%. Electroporation of eGFP was more efficient, transfecting 30% of tumoroid cells for the tumoroid line used. Given the importance of preserving the cellular heterogeneity found in patient samples and recapitulated in tumoroid models, these lower delivery efficiencies indicate that lipofection- and electroporation-based methods are not ideal for the generation of stably engineered tumoroid models. In contrast, lentiviral transduction at high MOI was the most efficient method for eGFP overexpression, initially transducing 67% of cells and enabling stable pool reporter line generation with nearly identical mutational profile and gene expression compared to the parental population. In follow up experiments, transduction also enabled generation of eGFP-expressing breast and endometrial reporter tumoroid lines. Overall, our results indicate that electroporation may be more suited for transient transfection across a wide range of payloads, and siRNA, gRNA, and Cas9 protein were able to be delivered by electroporation in follow up experiments. Lentivirus-based transduction is more suitable for generation of stable tumoroid pools. The insights gained from this study can be applied to tumoroids derived from various tissues, potentially accelerating advancements in cancer research and personalized medicine. Citation Format: Isha Dey, Xiaoyu Jenny Yang, Jacob Delgadillo, Garrett Wong, Colin D. Paul, Chris Yankaskas, Brittany Balhouse, Shyanne Salen, Sylvia Beam, Amber Bullock, Anthony Chatman, Pradip Shahi Thakuri, Kanika Singh, Jason Sharp, Matt Dallas, David Kuninger. Optimization of tumoroid size and payload delivery methods for the engineering of patient-derived tumoroid models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5193.

  PublisherDOI

• 428 Generation of a panel of patient-derived tumoroids for screening the potency of immunotherapies

  Regular and Young Investigator Award Abstracts · 2024-11-01

  articleOpen access

  <h3>Background</h3> Patient-derived tumoroids are self-assembled 3D cultures of primary cancer cells and are more physiologically relevant models of solid tumors than traditional 2D cell lines. Laborious culture protocols have limited the utilization of tumoroids in cancer immunotherapy research; to accelerate the use of these models, we developed Gibco™ OncoPro™ Tumoroid Culture Medium. Here, we derived 20 tumoroids across multiple indications (colorectal, lung, endometrial, and breast), capturing a wide range of gene mutations and transcriptome profiles, then utilized select models to evaluate the cytotoxicity of primary natural killer (NK) cells, human pluripotent stem cell (PSC)-derived NK cells (iNK), and chimeric antigen receptor (CAR)-T cells. <h3>Methods</h3> Tumoroids derived from primary cancer tissue were characterized by next-generation sequencing. Established tumoroids were cultured in an easy-to-handle suspension format, facilitating scale-up for biobanking, scale-down for assays, and automated liquid handling. Primary natural killer cells isolated from peripheral blood mononuclear cells (PBMCs) via negative selection were cultured in CTS™ NK-Xpander™ Medium. PSCs cultured in CTS™ StemScale™ PSC Suspension Medium were differentiated to hematopoietic progenitor cells and then iNK cells, which could be cryopreserved and expanded. CAR-T cells were generated by isolating primary T cells from PBMCs, knocking out endogenous T cell receptor by electroporating CRISPR-cas9/gRNA ribonucleoproteins, and knocking in CARs targeting Meso3 (region III of MSLN) or CD19 (as a control) using adeno-associated virus (AAV). <h3>Results</h3> Established tumoroids maintained phenotypic and genotypic signatures from their primary tumors. For cytotoxicity assays, tumoroids were dissociated, counted, and seeded into 96-well plates. For various assays, viable tumoroids were labelled with the mitochondrial membrane potential indicator, Image-iT™ TMRM, engineered to stably express green fluorescent protein (GFP), or seeded without labelling. After tumoroids expanded for 3–4 days, effector cells were added at a range of effector-to-target (E:T) ratios along with the caspase activity indicator, CellEvent™ Caspase 3/7. Time-lapse microscopy, image quantification, and cytokine analysis demonstrated immune cell-mediated cytotoxicity that depended on donor and dose. For CAR-T assays, the tumoroid biobank was leveraged to select tumoroids with high and low endogenous mesothelin expression, which was maintained from primary tumors. CD19 CAR-T cells did not kill CD19-negative tumoroid cells; similarly, Meso3 CAR-T cells effectively killed Meso3-positive, but not negative tumoroid cells, demonstrating specific and effective targeting. <h3>Conclusions</h3> Physiologically relevant patient-derived tumoroids may be used to evaluate the efficacy of immunotherapies in a medium-throughput format, providing a reliable, easy-to-use, and cost-effective tool for immuno-oncology screening, development, and quality control research.

  PublisherOA PDFDOI

• Long-term maintenance of patient-specific characteristics in tumoroids from six cancer indications in a common base culture media system

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-06-12 · 1 citations

  preprintOpen access1st authorCorresponding

  Abstract Tumoroids, also known as cancer organoids, are patient-derived cancer cells grown as 3D, self-organized multicellular structures that maintain key characteristics (e.g., genotype, gene expression levels) of the tumor from which they originated. These models have emerged as valuable tools for studying tumor biology, cytotoxicity, and response of patient-derived cells to cancer therapies. However, the establishment and maintenance of tumoroids has historically been challenging, labor intensive, and highly variable from lab to lab, hindering their widespread use. Here, we characterize the establishment and/or expansion of colorectal, lung, head and neck, breast, pancreas, and endometrial tumoroids using the standardized, serum-free Gibco OncoPro Tumoroid Culture Medium. Newly derived tumoroid lines ( n =20) were analyzed by targeted genomic profiling and RNA sequencing and were representative of tumor tissue samples. Tumoroid lines were stable for over 250 days in culture and freeze-thaw competent. Previously established tumoroid lines were also transitioned to OncoPro medium and exhibited, on average, similar growth rates and conserved donor-specific characteristics when compared to original media systems. Additionally, OncoPro medium was compatible with both embedded culture in extracellular matrix and growth in a suspension format for facile culture and scale up. An example application of these models for assessing the cytotoxicity of a natural killer cell line and primary natural killer cells over time and at various doses demonstrated the compatibility of these models with assays used in compound and cell therapy development. We anticipate that the standardization and versatility of this approach will have important benefits for basic cancer research, drug discovery, and personalized medicine and help make tumoroid models more accessible to the cancer research community.

  PublisherOA PDFDOI

• YAP localization mediates mechanical adaptation of human cancer cells during extravasation <i>in vivo</i>

  bioRxiv (Cold Spring Harbor Laboratory) · 2023-11-16 · 3 citations

  preprintOpen access

  Abstract Biophysical profiling of primary tumors has revealed that individual tumor cells fall along a highly heterogeneous continuum of mechanical phenotypes. One idea is that a subset of tumor cells is “softer” to facilitate detachment and escape from the primary site, a step required to initiate metastasis. However, it has also been postulated that cells must be able to deform and generate sufficient force to exit into distant sites. Here, we aimed to dissect the mechanical changes that occur during extravasation and organ colonization. Using multiplexed methods of intravital microscopy and optical tweezer based active microrheology, we obtained longitudinal images and mechanical profiles of cells during organ colonization in vivo . We determined that cells were softer, more liquid like upon exit of the vasculature but stiffened and became more solid like once in the new organ microenvironment. We also determined that a YAP mediated mechanogenotype influenced the global dissemination in our in vivo and in vitro models and that reducing mechanical heterogeneity could reduce extravasation. Moreover, our high throughput analysis of mechanical phenotypes of patient samples revealed that this mechanics was in part regulated by the external hydrodynamic forces that the cancer cells experienced within capillary mimetics. Our findings indicate that disseminated cancer cells can keep mutating with a continuum landscape of mechano-phenotypes, governed by the YAP-mediated mechanosensing of hydrodynamic flow.

  PublisherOA PDFDOI

Frequent coauthors

• Kandice Tanner

  59 shared

• Jack R. Staunton

  National Cancer Institute

  55 shared

• Hannah Burr

  Rensselaer Polytechnic Institute

  36 shared

• Kathryn M. Daly

  Florida Department of Agriculture and Consumer Services

  36 shared

• Alexus Devine

  National Cancer Institute

  28 shared

• Κωνσταντίνος Κωνσταντόπουλος

  Johns Hopkins University

  28 shared

• Raman Sood

  National Institutes of Health

  20 shared

• Kevin Bishop

  National Human Genome Research Institute

  20 shared

Awards & honors

• John and Emma Bonica Public Service Award from the American…
• Patient Advocacy Award from the American Academy of Pain Med…
• Mayday Pain and Society Fellow
• Hero by The Pain Community
• Pain Educator of the Year by the American Society of Pain Ed…