Fine-tuning the antigen sensitivity of CAR T cells: emerging strategies and current challenges

Chimeric antigen receptor (CAR) T cells are “living drugs” that specifically recognize their target antigen through an antibody-derived binding domain resulting in T cell activation, expansion, and destruction of cognate target cells. The FDA/EMA approval of CAR T cells for the treatment of B cell malignancies established CAR T cell therapy as an emerging pillar of modern immunotherapy. However, nearly every second patient undergoing CAR T cell therapy is suffering from disease relapse within the first two years which is thought to be due to downregulation or loss of the CAR target antigen on cancer cells, along with decreased functional capacities known as T cell exhaustion. Antigen downregulation below CAR activation threshold leaves the T cell silent, rendering CAR T cell therapy ineffective. With the application of CAR T cells for the treatment of a growing number of malignant diseases, particularly solid tumors, there is a need for augmenting CAR sensitivity to target antigen present at low densities on cancer cells. Here, we discuss upcoming strategies and current challenges in designing CARs for recognition of antigen low cancer cells, aiming at augmenting sensitivity and finally therapeutic efficacy while reducing the risk of tumor relapse

Magnetic CAR T cell purification using an anti-G4S linker antibody

Chimeric antigen receptor (CAR) redirected T cells are successfully employed in the combat against several hematological malignancies, however, are often compromised by low transduction rates making refinement of the CAR T cell products necessary. Here, we report a broadly applicable enrichment protocol relying on marking CAR T cells with an anti-glycine4-serine (G4S) linker antibody followed by magnetic activated cell sorting (MACS). The protocol is broadly applicable since the G4S peptide is an integral part of the vast majority of CARs as it links the VH and VL recognition domains. We demonstrate the feasibility by using the canonical second generation CARs specific for CEA and Her2, respectively, obtaining highly purified CAR T cell products in a one-step procedure without impairing cell viability. The protocol is also applicable to a dual specific CAR (tandem CAR). Except for CD39, T cell activation/exhaustion markers were not upregulated after separation. Purified CAR T cells retained their functionality with respect to antigen-specific cytokine secretion, cytotoxicity, and the capacity to proliferate and eliminate cognate tumor cells upon repetitive stimulation. Collectively, the one-step protocol for purifying CAR T cells extends the toolbox for preclinical research and specifically for clinical CAR T cell manufacturing

Primary Bone Marrow Large B-cell Lymphoma Presenting with Hemophagocytic Lymphohistiocytosis

Primary bone marrow lymphoma is an extremely rare disease. Its unusual clinical manifestations, such as hemophagocytic syndrome, frequently delay correct disease diagnosis, thus postponing treatment. Here, we reported a 76-year-old woman presenting with intermittent night fever and jaundice for 2 weeks, accompanied with hepatosplenomegaly and pancytopenia. Despite antibiotics treatment, the patient's fever persisted. Computed tomography showed hepatosplenomegaly without lymphadenopathy, and bone marrow aspiration and biopsy revealed a large B-cell lymphoma (LBCL) with hemophagocytic lymphohistiocytosis (HLH). After chemotherapy with rituximab, cyclophosphamide, vincristine, and prednisolone, both jaundice and pancytopenia recovered to normal. After 6 cycles of chemotherapy, the patient remained in complete remission for 18 months after diagnosis. Our experience indicates that clinicians should consider performing a timely bone marrow examination on patients with unknown fever and pancytopenia, particularly given that delayed diagnosis of primary bone marrow lymphoma can make treatment of this rare disease substantially more challenging

Autologous stem cell transplantation in multiple myeloma: Post-transplant outcomes of Taiwan Blood and Marrow Transplantation Registry

Background/Purpose: Multiple myeloma (MM) is a monoclonal plasma cell malignancy. The primary choice of treatment for MM is induction therapy followed by autologous stem cell transplantation (ASCT). This study aimed to analyze the treatment efficacy of ASCT in a Taiwanese cohort and evaluate possible prognostic factors. Methods: From the database of the Taiwan Blood and Marrow Transplantation registry, data on 396 patients with MM who underwent ASCT were reviewed. Results: The average age of participants was 54.8 years, and there were more men than women (57.6% vs. 42.4%). Most patients were diagnosed with IgG-type myeloma (52.4%), followed by IgA-type (23.2%) and light-chain type (21.4%). Patients with Durie Salmon Staging System (DSS) III disease accounted for 61.9% of the study cohort, while 23.7% had stage II and 14.4% had stage I disease. The median progression-free survival (PFS) and overall survival (OS) after ASCT were 46.5 months and 70.4 months, respectively. DSS III was a poor prognostic factor affecting both PFS and OS with a duration of 35.9 months and 69.0 months, respectively, compared with the other two stages (p = 0.006 and p = 0.03, respectively). In addition, patients with better treatment response before ASCT had better PFS and OS compared with those who did not show a response (both p < 0.0001). The overall incidence of organ toxicities associated with transplantation was low. Conclusion: In conclusion, our cohort showed that myeloma patients with early DSS and better treatment response before ASCT had better long-term survival outcomes. Keywords: Multiple myeloma, Transplantation, Surviva