Pembrolizumab enhances CAR T-cell persistence in relapsed ALL

The patient was reinfused a third time, and pembrolizumab was added to the regimen every 3 weeks. The patient is experiencing prolonged persistence and continued B-cell aplasia.

Patient 4 – Pembrolizumab for poor persistence

This patient had achieved a CR with murine CAR19, but had a CD19+ relapse at 9 months. The patient then received huCART19, had good proliferation and achieved a CR, but had short persistence and B-cell recovery at 2 months.

The patient relapsed at 12 months and was reinfused with huCART19 at 14 months.

Pembrolizumab was added on day 14 after reinfusion, but the patient had no huCART19 proliferation, no response, and CD19+ MRD.

Patient 5 – Pembrolizumab for poor persistence

The patient responded to a prior murine CART19, but had a CD19+ relapse at 12 months.

The patient was infused with huCART19 and had good proliferation but short persistence. The patient was reinfused at 6 months, but again had short persistence.

The patient was reinfused again at 8 months because of B-cell recovery, and pembrolizumab was added on day 14 and administered every 3 weeks thereafter.

The patient is experiencing prolonged persistence and continued B-cell aplasia.

Patient 6 – Pembrolizumab for lymphomatous disease

This patient, who had widespread lymphadenopathy and M3 bone marrow, had not received prior CAR T cells and was treated for the first time with a murine CART19 for r/r ALL.

The patient had good expansion of CART19, but by day 28, PET scan showed widespread lymph node disease despite CR in the bone marrow.

The patient was given pembrolizumab on day 32 after infusion and every 2-3 weeks thereafter. After the addition of pembrolizumab, the patient had increased CART19 cells in blood and a significant decrease in PET-avid disease.

Summary

Three of six patients achieved objective clinical responses with pembrolizumab: 2 had prolonged B-cell aplasia, and another had a decrease in PET-avid lymphomatous disease.

The addition of pembrolizumab was also well tolerated by the patients, with minimal side effects of fever in 2 patients, cytopenias in 2 patients, and no instances of severe CRS.

The investigators believe the addition of checkpoint pathway inhibitors has the potential to prolong CAR T-cell persistence and warrants further investigation.