GC-02. Resistance to anti-CD19 CAR T-cell therapy. Case report

Summary

Primary resistance to CAR T-cell therapy occurs in 10-20% of pediatric B-ALL cases [PA Atilla, 2022]. Impaired functional activity of CAR T-cells and biological properties of leukemic cells are among the causes of described phenomenon. Anti-CD19 CAR T-cell therapy was carried out at Belarusian Research Center for Pediatric Oncology, Hematology and Immunology (BRCPOHI) for 8 B-ALL patients with one case proven to have primary resistance to the given therapy.

Materials and methods

A 7-year old boy was diagnosed with B-ALL, positive for MLL (KMT2A) gene rearrangement (MLL-AF9), BIII immunophenotype positive for NG2, CD33, CD65 and CD15 expression. Short-term remission was achieved after treatment according to ALL-MB-2015 protocol with subsequent isolated bone marrow (BM) early relapse I. Leukemic cells were still positive for MLL-AF9, but immunophenotype changed to BI with CD33 and CD15 expression. Anti-relapse treatment failed to induce remission. Moreover, leukemic clone acquired multi-drug resistance to chemotherapy. The decision was made to perform anti-CD19 CAR T-cell therapy. Taking into account high tumor burden (93% of blast cells in BM) and patient general condition, final dose of CAR-T-cells (1×10⁶ cells/kg) was given as fractionated infusions of 10% and 90% over 7 days. Immune monitoring did not reveal significant CAR T-cell expansion in recipient BM or peripheral blood (PB). Peak concentration of CAR T-cells in patient PB was 0.05 cells/μl, while median value in group of 7 patients with noticed expansion was 17 cells/μl [range 1.7-224]. Despite carried out immunotherapy, growth of leukemic blasts’ count was observed in PB and BM. Immunophenotyping of leukemic cells at this stage revealed mixed phenotype (B/My). Patient died of the disease progression 30 days after the last injection of CAR-T-cells.

Results

It is well known that efficiency of CAR T-cell therapy depends dramatically on cell product characteristics. High content of exhausted and terminally differentiated T-cells significantly reduce their potential for expansion and persistence in vivo. In described case number of CCR7-positive CD4 and CD8 T-cells in final product was 84% and 90% correspondingly. Moreover, CAR-T-cells demonstrated high in vitro cytotoxicity against model cell line and recipient leukemic blasts. It was previously reported that multi-lineage phenotype (CD19, CD20, CD33, CD34) is frequent in CAR T-cell therapy non-responders [KE Masih, 2022]. It must be noticed, that B/My phenotype was also observed in described patient. Another one mechanism of primary resistance to CAR-T-cell therapy is CD58 gene mutations or loss of corresponding protein expression on tumor cells [RG Majzner, 2020, Xin Yan, 2022]. CD58 protein is a ligand for T-cell costimulatory receptor CD2. Disruption of CD58 interaction with its partner CD2 leads to formation of suboptimal immunological synapse, which results in impairment of CAR T-cell functional activity and loss of its expansion potential. Normalized to healthy lymphocytes, coefficient of CD58 expression on the surface of given patient blasts was 0.95. Whereas median value for the same parameter in group of CAR T-therapy responders was 2.46 (range 1.2-6.56).

Conclusions

We suppose that the described case of primary resistance of B-ALL to anti-CD19 CAR T-cell therapy can be explained by patient’s leukemic cells properties: mixed immunophenotype and rearrangement of MLL gene, decreased expression/loss of surface CD58 antigen.

Keywords

Total body irradiation, allo-HSCT, children, hemoblastoses, radiation therapy.