Clinical Responses in Patients Infused with T Lymphocytes Redirected to Target Kappa-Light Immunoglobulin Chain

Adoptive transfer of T cells with a CD19-specific chimeric antigen receptor (CAR) to treat B-cell­ malignancies shows remarkable clinical efficacy. However, long-term persistence of T cells targeting CD19, a pan-B cell marker, causes depletion of normal B cells and consequent severe hypogammaglobulinemia. In order to target B-cell malignancies more selectively, we have taken advantage of the clonal restriction of mature B-cell malignancies, which express either a κ or a λ-light immunoglobulin chain. We generated a CAR specific for κ-light chain (CAR.κ) to selectively target κ⁺ lymphoma/leukemia cells, while sparing the normal B cells expressing the non-targeted λ-light chain, thus minimizing the impairment of humoral immunity. After validation in preclinical experiments, we designed a phase I clinical trial in which patients with refractory/relapsed κ⁺ NHL/CLL are infused with autologous T cells expressing a CAR.κ that includes a CD28 costimulatory domain. The protocol also allows for the inclusion of patients with multiple myeloma (MM) with the aim of targeting putative myeloma initiating cells. Three dose levels (DL) are being assessed: 0.2 (DL1), 1 (DL2) and 2 (DL3) ×10⁸ T cells/m².

T cells were generated for 13 patients by activating autologous PBMC with OKT3 (n=5) or CD3/CD28 monoclonal antibodies (n=8). In 2 patients with >95% circulating CLL cells, CD3 positive selection was performed using CliniMACS. After transduction, T cells (1.2×10⁷±0.5×10⁷) were expanded ex vivo for 18±4 days in the presence of IL-2 to reach sufficient numbers for dose escalation. CAR expression was 81%±13% by flow cytometry. Products were composed predominantly of CD8⁺ cells (78%±10%). CAR⁺ T cells specifically targeted κ⁺ tumors (specific lysis by ⁵¹Cr release 79%±10%, 20:1 E:T ratio) but not κ^– tumors (11%±7%) or the NK-sensitive cell line K562 (26%±13%). Ten patients were treated so far: 2 on DL1, 3 on DL2 and 5 on DL3. Any other treatments were discontinued at least 4 weeks prior to T-cell infusion and patients with ALC >500 received 12.5 mg/kg cyclophosphamide 4 days before infusion. Infusions were well tolerated without side effects. A CAR.κ-specific Q-PCR assay showed that molecular signals peaked 1-2 weeks post infusion and remained detectable for at least 6 weeks and up to 9 months in 1 patient. Of the 5 patients with relapsed NHL, 2 entered complete remission (after 2 and 3 infusions at DL1 and DL3, respectively), 1 had a partial response and 2 progressed; 3/3 patients with MM have had stable disease for 2, 11 and 17 months, associated with up to 38% reduction in their paraprotein; and 2/2 patients with CLL progressed before or shortly after the 6 week evaluation. 

In conclusion, our data indicate that infusion of CAR.κ⁺ T cells is safe at every DL and can be effective in patients with κ⁺ lymphoma.