Clinical responses with T lymphocytes targeting malignancy-associated κ light chains

Abstract

Background: Treatment of B cell malignancies with adoptive transfer of T cells with a CD19-specific chimeric antigen receptor (CAR) shows remarkable clinical efficacy. However, long-term persistence of T cells targeting CD19, a pan-B cell marker, also depletes normal B cells and causes severe hypogammaglobulinemia. Here, we developed a strategy to target B cell malignancies more selectively by taking advantage of B cell light Ig chain restriction. We generated a CAR that is specific for the κ light chain (κ.CAR) and therefore recognizes κ-restricted cells and spares the normal B cells expressing the nontargeted λ light chain, thus potentially minimizing humoral immunity impairment.

Methods: We conducted a phase 1 clinical trial and treated 16 patients with relapsed or refractory κ+ non-Hodgkin lymphoma/chronic lymphocytic leukemia (NHL/CLL) or multiple myeloma (MM) with autologous T cells genetically modified to express κ.CAR (κ.CARTs). Other treatments were discontinued in 11 of the 16 patients at least 4 weeks prior to T cell infusion. Six patients without lymphopenia received 12.5 mg/kg cyclophosphamide 4 days before κ.CART infusion (0.2 × 108 to 2 × 108 κ.CARTs/m2). No other lymphodepletion was used.

Results: κ.CART expansion peaked 1-2 weeks after infusion, and cells remained detectable for more than 6 weeks. Of 9 patients with relapsed NHL or CLL, 2 entered complete remission after 2 and 3 infusions of κ.CARTs, and 1 had a partial response. Of 7 patients with MM, 4 had stable disease lasting 2-17 months. No toxicities attributable to κ.CARTs were observed.

Conclusion: κ.CART infusion is feasible and safe and can lead to complete clinical responses.

Trial registration: ClinicalTrials.gov NCT00881920.

Funding: National Cancer Institute (NCI) grants 3P50CA126752 and 5P30CA125123 and Leukemia and Lymphoma Society (LLS) Specialized Centers of Research (SCOR) grant 7018.

Figure 1. Flow chart of clinical trial NCT00881920 (CHARKALL).

Figure 2. In vivo expansion and persistence of infused κ.CARTs.

In vivo expansion and persistence of infused κ.CARTs was assessed by qPCR of peripheral blood from patients with NHL or CLL (A) and from patients with MM (B). Data points represent critical post-infusion intervals after the first infusion of κ.CARTs. There was no significant difference in the AUC for additional infusions (Supplemental Figure 2). Dotted lines denote each patient (color key shows universal patient identifier numbers [UPINs]), and the continuous line summarizes the mean expansion and persistence (error bars represent the standard deviation).

Figure 3. Biological effects observed after κ.CART infusion.

After κ.CART infusion, a transient decline in total B cell numbers and in the κ/λ ratio in MM patients (n = 8, paired Student’s t test) was observed (A). In general, there was a decrease in the mean fluorescence intensity of κ light chain expression during the first 2 weeks after κ.CART infusion; data from 1 representative patient are shown in B, with κ.CART expansion data in the top panel and κ light chain expression data in the bottom panels. Numbers in the dot plots correspond to the percentage of CD19⁺ (upper left quadrant) and CD3⁺ (lower right quadrant) PBMCs; histogram shows the distribution of the intensity of surface κ light chain staining in CD19⁺ PBMCs, highlighting the κ^– (left peak) and κ⁺ (right peak) population, at each of the time points depicted. Inflammatory cytokines levels (shown for IL-6) increased modestly after κ.CART infusion (C), in both NHL (n = 17 infusions) and MM (n = 10 infusions) patients (paired Student’s t test), and no clinical evidence of CRS was observed. There was no significant generation of HAMAs after κ.CART infusion (D).

Figure 4. Patient 2 achieved a durable CR after 2 infusions of κ.CARTs.

Patient 2 had transformed follicular lymphoma (FL) with active disease in the neck 4 weeks after receiving 1 dose of bendamustine, as documented in the preinfusion PET/CT scan, which showed a hypermetabolic 7.2 × 3.4-cm left anterior mass (circled) and a hypermetabolic 1.7 × 1-cm left paratracheal lymph node. Six weeks after the first infusion of κ.CARTs, a PET/CT scan showed a PR, with a decrease in the activity and size of the mass (2.4 × 0.8 cm) and lymph node (1.3 × 0.6 cm). Another PET scan obtained after a second infusion was consistent with a CR. This patient has been without evidence of disease for almost 3 years.

Figure 5. Patient 9 achieved a transient CR after 3 infusions of κ.CARTs.

Patient 9 had transformed FL with active disease in the retroperitoneum and pelvis, including a 2.1 × 1.2-cm left external iliac lymph node near the anterior aspect of the left acetabulum, with a standard uptake value (SUV) of 8.5 (bottom row) and a 1 × 1-cm posterior left common iliac chain lymph node, with an SUV of 4.4 (top row). Six weeks after the first infusion of κ.CARTs, a repeat PET/CT scan showed interval improvement in uptake and, to a lesser degree, in the size of multiple lymph nodes, including mild interval improvement in uptake (SUV 5.5) and size (2 × 0.9-cm) in the external iliac lymph node and improved uptake (SUV 3.4) and a slight decrease in the size of the common iliac lymph node. Six weeks after the second infusion of κ.CARTs, we observed a significant response with what appeared to be residual disease within the left pelvic lymph nodes, with the external iliac lymph node that had remained stable in size but had decreased to an SUV of 2.9 and the common iliac lymph node with an SUV of 2.2. Six weeks after the third infusion of κ.CARTs, there was a decrease in the size (the external iliac lymph node was 1.7 × 0.9 cm) and resolution of the previous uptake within the left pelvic lymph nodes and normal uptake elsewhere, consistent with a CR.

Figure 6. Patient 7 had stabilization of disease after 2 infusions of κ.CARTs.

Patient 7 had active IgG MM at the time of κ.CART infusion. Afterward, she had a slow decrease (SD) in her monoclonal protein levels and improvement in her hemoglobin levels, which continued for 2 years, when she had evidence of disease progression. κLC, light chain.