Translational Analysis from CARTITUDE-1, an Ongoing Phase 1b/2 Study of JNJ-4528 BCMA-targeted CAR-T Cell Therapy in Relapsed and/or Refractory Multiple Myeloma (R/R MM), Indicates Preferential Expansion of CD8+ T Cell Central Memory Cell Subset

JNJ-4528 is a chimeric antigen receptor T cell (CAR-T) therapy containing two B-cell maturation antigen (BCMA)-targeting single-domain antibodies designed to confer avidity. We present translational data from the phase 1b cohort of an ongoing phase 1b/2 study conducted in the US to explore the safety and efficacy of JNJ-4528 in patients with R/R MM (NCT03548207).

Apheresis samples were collected from 25 patients, and T cells were selected and transduced with a lentivirus encoding the BCMA CAR construct. Immune cell composition of both the apheresis samples and transduced cells following expansion ("drug product" [DP]) was evaluated by multiparametric flow cytometry. The median proportion of CAR+ T cells in the DP was 16% (range 6-28%) of total cells, with a median proportion of 12% (range 4-22%) CD4+ CAR+ and 7% (range 3-20%) CD8+ CAR+ T cells. The CD4:CD8 ratio of CAR+ T cells in the DP was variable between patients, with a median of 1.5 (range 0.62-4.40). Significant variability between patients was observed in the composition of the DP regarding T cell subsets (i.e., naïve, Tscm, Tcm, Tem, Teff, Temra) although this profile was comparable in the CAR- and CAR+ T cell subpopulations within each patient.

Patients were administered a single infusion of the JNJ-4528 DP at a target dose of 0.75x10⁶ CAR+ T cells/kg (target range 0.5-1.0x10⁶). Of the 21 patients with a postbaseline disease evaluation, the overall response rate was 91% at a median follow-up of 3 months (range 1-10). Among the 15 patients with post-infusion day 28 evaluable bone marrow (BM) samples by next generation flow cytometry and/or next generation sequencing, 10 were minimal residual disease negative at the 10^-5 level of sensitivity, 2 at 10^-4 level of sensitivity, and 3 had unidentified clones. All patients expressed BCMA in BM tumor cells at baseline, as assessed by flow cytometry, although levels varied among patients. Clinical responses appear independent of BM BCMA expression.

Following infusion, CAR+ T cells expanded reaching a peak between 20-87% of the total T cells in blood between days 10-14 post-infusion. The CD4:CD8 ratio and the proportion of T cell memory subsets in the final DP did not correlate with peak CAR+ T cell expansion. Peak CAR+ T cell expansion did not correlate with response. Ten patients had a follow-up of enumeration of CAR+ T cells in blood of at least 8 weeks. In 5 patients, CAR+ T cells decreased to below the limit of quantification (BLOQ) of the flow cytometry assay (5 cells/µl) within 8 weeks (range 2-7) post-infusion. Although preliminary, no difference was observed in the response rate between these patients compared with patients with measurable CAR+ T cells after 8 weeks. A similar trend was observed when expansion and persistence were assessed by measuring transgene levels.

While both CD4+ and CD8+ CAR+ T cells expanded in vivo, the CD4:CD8 CAR+ ratio decreased at peak expansion compared with the final DP (from a median of 1.35 to 0.35), indicating a preferential expansion of CD8+ CAR+ T cells in blood. At peak expansion, CD8+ CAR+ T cells showed predominantly a central memory (Tcm) phenotype (CCR7+ CD45RO+; median of 90% [range 29.3-98.5%]). In contrast, CD4+ CAR+ T cells were enriched in effector memory (Tem) cells (CCR7- CD45RO+; median of 87% [range 69.5-98.1%]) at peak expansion. A similar trend in the CD4:CD8 ratio, as well as the T cell memory subset composition, was observed in BM of all 11 patients with evaluable samples at day 28.

CD8+ CAR- T cells showed an approximate 50:50 ratio of stem memory (Tscm):Tcm subsets while CD4+ CAR- T cells showed an approximate 50:50 ratio of Tcm:Tem subsets, indicating a differential T cell maturation course for CD4+ and CD8+ CAR+ and CAR- T cells.

Expansion of CAR+ T cells correlated with increases in serum cytokines levels (i.e., IL-6, IFNγ, IL-10) which peaked around day 10, coinciding with maximal expansion of CAR+ T cells. Generally, increases in some proinflammatory cytokines (i.e., IL-6) correlated with onset of cytokine release syndrome symptoms (median time to onset of 7 days [range 2-12]).

Findings from the ongoing CARTITUDE-1 trial suggest that JNJ-4528 is a differentiated CAR-T cell therapy that is highly active at a relatively low dose, potentially related to a preferential and consistent in vivo expansion of CD8+ CAR+ T cells displaying a central memory phenotype.