CAR T Expansion

“CAR T-cell expansion occurred despite the absence of lymphodepletion,” Dr. Ho said. “All patients experienced a rise in lymphocyte count…CAR-positive T cells were detected in the blood on Day 15 at levels of 22% to 85% of CD3-positive T cells, with a mixture of CD4 and CD8 cells of different proportions. Of note, the highest level of 85% was achieved at dose level –1,” she reported.

Phenotypically, in all four patients, KLN-1010 generated CAR Ts that were enriched with less differentiated T cells and with memory CAR T cells, which are known to be associated with improved expansion, persistence, and tumor control associated with durable remission.The Cmax and the persistence of the CAR T cells seen out to 3 months, in both blood and marrow, were commensurate with the available ex vivo products. The level of expansion was 51,000 to 108,000 copies per microgram of DNA.

All patients achieved MRD negativity within 1 month of treatment: the first three achieved MRD-negative disease at 10-6 sensitivity, while the fourth patient, who was treated at dose level –1, had MRD negativity at a sensitivity of 10-5 at month 1. Two patients remained MRD-negative at 3 months, one patient at 10-6 and one at 10-5. Dr. Ho explained the sensitivity at 10-5 was “due to sample cellularity by flow cytometry,” and sequencing is now in progress.

The patient with the longest follow-up (approximately 5 months) achieved a complete response by International Myeloma Working Group (IMWG) criteria. The remaining patients were in partial response, attributed to delayed clearance of paraprotein, with additional evidence of activity demonstrated by marked reductions in involved free light chains and soluble BCMA levels, consistent with a reduction in tumor load, Dr. Ho reported.

Good Tolerability

No cases of immune effector cell–associated neurotoxicity syndrome (ICANS) were observed in these four participants. Three cases of cytokine release syndrome occurred, and all were grade 1 or 2. One case of transient grade 4 neutropenia, attributed to margination, was reported. In addition, one patient developed grade 3 anemia and one developed grade 1 thrombocytopenia. Infusion reactions occurred in three patients, with only one grade 3 event, all resolving promptly with standard management. Compared to ex vivo CAR T-cell therapy, this indicates an improved adverse event profile, according to Dr. Ho. 

Results: Patients (N=3) ranged from age 61-72 and their time from diagnosis was 7.9-9.4 yrs. All had highrisk cytogenetics and 3-4 prior lines of therapy. Two were refractory to a PI, an IMiD, and anti-CD38 therapy. All were naïve to BCMA-targeted therapies; none had extramedullary involvement. Time from consent to infusion was 13-18 days.

All patients experienced treatment-emergent adverse events (AEs), primarily around infusion and during CAR-T expansion. Two patients developed infusion-related reaction (IRR) 30-60 min post-infusion that resolved within 6-48 hrs. Tocilizumab was administered prophylactically in the latter two patients after the first IRR was observed. Grade 2 cytokine release syndrome (CRS) was observed in two patients during CAR-T expansion. No immune effector cell-associated neurotoxicity syndrome or delayed neurotoxicity (e.g. parkinsonism or cranial nerve palsies) were noted. Cytopenias were limited: one patient with Grade 3 anemia lasting 1 day (day 15) and one patient with Grade 3/4 neutropenia (only on days 1 and 15). No patients were observed to have Grade ≥3 thrombocytopenia, Grade ≥3 hematologic toxicity, or treatment-emergent infections at month 1.

T cell expansion occurred despite no preparative chemotherapy with peak absolute lymphocyte counts (ALC) between days 13-18 at 2.3, 7.37, and 43.1 × 10 9 /L. CAR-positive cells comprised 35%, 22%, and 72% of CD3+ lymphocytes on day 15 with vector transgene copies of 51,647 and 65,873 copies/µg genomic DNA in the two samples analyzed. No clinical sequelae of the lymphocytosis were noted; dexamethasone promptly resolved the lymphocytosis in the patient with the highest ALC. CAR-T cells were detected in the BM and peripheral blood through month 3 and were comprised predominantly of memory-phenotype T cells.

All patients experienced an MRD-negative response (10 -5 or 10 -6 sensitivity) at month 1 by a nextgeneration flow cytometry or sequencing method. The patient with the longest follow-up to date maintained the MRD negativity (10 -6 sensitivity) at month 3. All achieved a partial response at month 1 by IMWG criteria that deepened over time; the best response was a very good partial response (VGPR) at month 3. All remain in response without disease progression.

Conclusions: Preliminary results from the first three patients dosed in the inMMyCAR Phase 1 study of KLN-1010 demonstrate that promising clinical activity and manageable toxicities are feasible with an offthe-shelf in vivo CAR-T in MM. Lymphodepletion was not required for in vivo CAR-T cell generation and expansion in the peripheral blood. CRS was consistent with that seen with ex vivo CAR-T therapies, while cytopenias were notably limited and no treatment-emergent infections occurred. Early MRD-negative responses with deepening of IMWG response over time and persistent memory CAR-T cells were observed. Similar outcomes have been associated with durable remissions with ex vivo CAR-T cells in MM. CAR-T cell expansion peaked around day 15; memory-phenotype T cells persisted in the BM and blood through month 3. All patients had an early MRD-negative BM that was sustained for >3 months in the patient with the longest follow up. The study remains ongoing and updated results will be presented.