Potency assays and biomarkers for cell-based advanced therapy medicinal products

Advancing CAR T-cell therapies: Preclinical insights and clinical translation for hematological malignancies

Chimeric antigen receptor (CAR) T-cell therapy has achieved significant success in achieving durable and potentially curative responses in patients with hematological malignancies. CARs are tailored fusion proteins that direct T cells to a specific antigen on tumor cells thereby eliciting a targeted immune response. The approval of several CD19-targeted CAR T-cell therapies has resulted in a notable surge in clinical trials involving CAR T cell therapies for hematological malignancies. Despite advancements in understanding response mechanisms, resistance patterns, and adverse events associated with CAR T-cell therapy, the translation of these insights into robust clinical efficacy has shown modest outcomes in both clinical trials and real-world scenarios. Therefore, the assessment of CAR T-cell functionality through rigorous preclinical studies plays a pivotal role in refining therapeutic strategies for clinical applications. This review provides an overview of the various in vitro and animal models used to assess the functionality of CAR T-cells. We discuss the findings from preclinical research involving approved CAR T-cell products, along with the implications derived from recent preclinical studies aiming to optimize the functionality of CAR T-cells. The review underscores the importance of robust preclinical evaluations and the need for models that accurately replicate human disease to bridge the gap between preclinical success and clinical efficacy.

Production of donor-derived cytotoxic T lymphocytes with potent anti-leukemia activity for adoptive immunotherapy in high-risk pediatric patients given haploidentical hematopoietic stem cell transplantation

BACKGROUND AIMS

Somatic cell therapy based on the infusion of donor-derived cytotoxic T lymphocytes (CTL) able to recognize patients' leukemia blasts (LB) is a promising approach to control leukemia relapse after allogeneic HSCT. The success of this approach strongly depends on the ex vivo generation of high-quality donor-derived anti-leukemia CTL in compliance with Good Manufacturing Practices (GMP). We previously described a procedure for generating large numbers of donor-derived anti-leukemia CTL through stimulation of CD8-enriched lymphocytes with dendritic cells (DCs) pulsed with apoptotic LB in the presence of interleukin (IL)-12, IL-7 and IL-15. Here we report that the use of IFN-DC and the addition of IFNα2b during the priming phase significantly improve the generation of an efficient anti-leukemia T cells response in vitro.

METHODS

Using this approach, 20 high-risk pediatric patients given haploidentical HSCT for high-risk acute leukemia were enrolled and 51 batches of advanced therapy medical products (ATMP), anti-leukemia CTL, were produced.

RESULTS

Quality controls demonstrated that all batches were sterile, free of mycoplasma and conformed to acceptable endotoxin levels. Genotype analysis confirmed the molecular identity of the ATMP based on the starting biological material used for their production. The majority of ATMP were CD3+/CD8+ cells, with a memory/terminal activated phenotype, including T-central memory populations. ATMP were viable after thawing, and most ATMP batches displayed efficient capacity to lyse patients' LB and to secrete interferon-γ and tumor necrosis factor-α.

CONCLUSIONS

These results demonstrated that our protocol is highly reproducible and allows the generation of large numbers of immunologically safe and functional anti-leukemia CTL with a high level of standardization.

In vitro CAR-T cell killing: validation of the potency assay

For advanced therapy medicinal products, the development and validation of potency assays are required, in accordance with international guidelines, to characterise the product and obtain reliable and consistent data. Our purpose was to validate the killing assay for the evaluation of autologous anti-CD19 chimeric antigen receptor (CAR) T potency. We used CD4 + and CD8 + lymphocytes or anti-CD19 CAR-T cells as effector cells and REH (CD19 +) or MOLM-13 (CD19 -) cell lines as target cells. After co-culturing target and effector cells (1:1 ratio) for 24 h, samples were labelled with 7-AAD, anti-CD3 and anti-CD19 antibodies and the frequency of CD19 + dead cells was evaluated by flow cytometry. In order to verify the CAR-T specificity for the CD19 + target, the co-culture between CAR-T and REH or MOLM-13 at different effector-to-target ratios was scheduled. Moreover, not transduced CD4 + and CD8 + lymphocytes were tested in comparison with CAR-T from the same donor to demonstrate the assay specificity. Linearity and accuracy were evaluated, and established acceptance criteria were compiled for both parameters (r2 ≥ 0.97 for linearity and average relative error ≤ 10% for accuracy). Furthermore, the method was considered robust when performed between 23 and 25 h of co-culture, and the intra-assay, inter-assay and inter-day precision was obtained. Finally, in order to verify the inter-analyst precision, the test was executed by three different operators and the intra-class correlation coefficient was > 0.4 in both cases. In conclusion, we consider this CAR-T potency assay as validated and usable in all steps of product development and quality control.

Mesenchymal Stromal Cell-Based Products: Challenges and Clinical Therapeutic Options

Mesenchymal stromal cell (MSC)-based advanced therapy medicinal products (ATMPs) are being tried in a vast range of clinical applications. These cells can be isolated from different donor tissues by using several methods, or they can even be derived from induced pluripotent stem cells or embryonic stem cells. However, ATMP heterogeneity may impact product identity and potency, and, consequently, clinical trial outcomes. In this review, we discuss these topics and the need to establish minimal criteria regarding the manufacturing of MSCs so that these innovative therapeutics may be better positioned to contribute to the advancement of regenerative medicine.

Biomarkers of Efficacy and Safety of the Academic BCMA-CART ARI0002h for the Treatment of Refractory Multiple Myeloma

PURPOSE

B-cell maturation antigen (BCMA)-chimeric antigen receptor T-cells (CART) improve results obtained with conventional therapy in the treatment of relapsed/refractory multiple myeloma. However, the high demand and expensive costs associated with CART therapy might prove unsustainable for health systems. Academic CARTs could potentially overcome these issues. Moreover, response biomarkers and resistance mechanisms need to be identified and addressed to improve efficacy and patient selection. Here, we present clinical and ancillary results of the 60 patients treated with the academic BCMA-CART, ARI0002h, in the CARTBCMA-HCB-01 trial.

PATIENTS AND METHODS

We collected apheresis, final product, peripheral blood and bone marrow samples before and after infusion. We assessed BCMA, T-cell subsets, CART kinetics and antibodies, B-cell aplasia, cytokines, and measurable residual disease by next-generation flow cytometry, and correlated these to clinical outcomes.

RESULTS

At cut-off date March 17, 2023, with a median follow-up of 23.1 months (95% CI, 9.2-37.1), overall response rate in the first 3 months was 95% [95% confidence interval (CI), 89.5-100]; cytokine release syndrome (CRS) was observed in 90% of patients (5% grades ≥3) and grade 1 immune effector cell-associated neurotoxicity syndrome was reported in 2 patients (3%). Median progression-free survival was 15.8 months (95% CI, 11.5-22.4). Surface BCMA was not predictive of response or survival, but soluble BCMA correlated with worse clinical outcomes and CRS severity. Activation marker HLA-DR in the apheresis was associated with longer progression-free survival and increased exhaustion markers correlated with poorer outcomes. ARI0002h kinetics and loss of B-cell aplasia were not predictive of relapse.

CONCLUSIONS

Despite deep and sustained responses achieved with ARI0002h, we identified several biomarkers that correlate with poor outcomes.

Potency assay to predict the anti-inflammatory capacity of a cell therapy product for macrophage-driven diseases: overcoming the challenges of assay development and validation

BACKGROUND

Given the high level of product complexity and limited regulatory guidance, designing and implementing appropriate potency assays is often the most challenging part of establishing a quality control testing matrix for a cell-based medicinal product. Among the most elusive tasks are the selection of suitable read-out parameters, the development of assay designs that most closely model the pathophysiological conditions, and the validation of the methods. Here we describe these challenges and how they were addressed in developing an assay that measures the anti-inflammatory potency of mesenchymal stromal cells (MSCs) in an M1 macrophage-dominated inflammatory environment.

METHODS

An in vitro inflammation model was established by coculturing skin-derived ABCB5+ MSCs with THP-1 monocyte-derived M1-polarized macrophages. Readout was the amount of interleukin 1 receptor antagonist (IL-1RA) secreted by the MSCs in the coculture, measured by an enzyme-linked immunosorbent assay.

RESULTS

IL-1RA was quantified with guideline-concordant selectivity, accuracy and precision over a relevant concentration range. Consistent induction of the macrophage markers CD36 and CD80 indicated successful macrophage differentiation and M1 polarization of THP-1 cells, which was functionally confirmed by release of proinflammatory tumor necrosis factor α. Testing a wide range of MSC/macrophage ratios revealed the optimal ratio for near-maximal stimulation of MSCs to secrete IL-1RA, providing absolute maximum levels per individual MSC that can be used for future comparison with clinical efficacy. Batch release testing of 71 consecutively manufactured MSC batches showed a low overall failure rate and a high comparability between donors.

CONCLUSIONS

We describe the systematic development and validation of a therapeutically relevant, straightforward, robust and reproducible potency assay to measure the immunomodulatory capacity of MSCs in M1 macrophage-driven inflammation. The insights into the challenges and how they were addressed may also be helpful to developers of potency assays related to other cellular functions and clinical indications.

A novel multicolor fluorescent spot assay for the functional assessment of chimeric antigen receptor (CAR) T-cell products

BACKGROUND AIMS

Chimeric antigen receptor (CAR) T-cell (CAR-T) therapies have revolutionized the treatment of B-cell lymphomas. Unfortunately, relapses after CD19-targeted CAR-T are relatively common and, therefore, there is a critical need for assays able to assess the function and potency of CAR-T products pre-infusion, which will hopefully help to optimize CAR-T therapies. We developed a novel multicolor fluorescent spot assay (MFSA) for the functional assessment of CAR-T products on a single-cell level, combining the numerical assessment of CAR-T products with their functional characterization.

METHODS

We first used a standard single-cell interferon (IFN)-γ enzyme-linked immune absorbent spot assay to measure CD19-targeted CAR-T responses to CD19-coated beads. We then developed, optimized and validated an MFSA that simultaneously measures the secretion of combinations of different cytokines on a single CAR-T level.

RESULTS

We identified IFN-γ/tumor necrosis factor-α/granzyme B as the most relevant cytokine combination, and we used our novel MFSA to functionally and numerically characterize two clinical-grade CAR-T products.

CONCLUSIONS

In conclusion, we have developed a novel assay for the quantitative and functional potency assessment of CAR-T products. Our optimized MFSA is cost-effective, easy to perform, reliable, can be performed overnight, allowing for a fast delivery of the product to the patient, and requires relatively minimal maintenance and training. The clinical value of our novel assay will be assessed in studies correlating the pre-infusion assessment of CAR-T products with the patients' outcome in a prospective fashion.

Beneath the radar: immune-evasive cell sources for stroke therapy

Stem cell therapy is an emerging treatment paradigm for stroke patients with remaining neurological deficits. While allogeneic cell transplants overcome the manufacturing constraints of autologous grafts, they can be rejected by the recipient's immune system, which identifies foreign cells through the human leukocyte antigen (HLA) system. The heterogeneity of HLA molecules in the human population would require a very high number of cell lines, which may still be inadequate for patients with rare genetic HLAs. Here, we outline key progress in genetic HLA engineering in pluripotent stem and derived cells to evade the host's immune system, reducing the number of allogeneic cell lines required, and examine safety measures explored in both preclinical studies and upcoming clinical trials.