BCMA emerging as a promising target in MM

Dr Cohen is scheduled to report the preliminary data on the cyclophosphamide cohorts (cohorts 2 and 3) at ASH 2017. Those cohorts, he said, are showing a bit more persistence and increased frequency of responses.

Other BCMA-specific CAR trials

Another BCMA CAR, bb2121, consists of a human anti-BCMA scFv, a lentiviral vector, and a CD3/4-1BB costimulatory domain.

In the first-in-human trial of bb2121* (NCT02658929), all 21 patients received cyclophosphamide and fludarabine conditioning first.

There were “very impressive response rates in this study,” Dr Cohen said.

Once patients were dosed at the higher levels of 150 million cells or greater, every patient responded.

“Many responses are still durable,” he pointed out, “some approaching a year.”

LCAR-B38M is structurally different from the other BCMA-specific CARs. It has 2 binding sites for BCMA.

Thirty-five patients enrolled on the trial of LCAR-B38M (NCT03090659), and 19 were evaluable for response.

Patients had a median of 3 or 4 lines of prior therapy. All received cyclophosphamide alone as conditioning.

All 19 evaluable patients responded, and 14 (74%) achieved an sCR.

Dr Cohen noted the differences among the 4 trials: costimulatory domains varied, the Penn study did not require a pre-existing level of BCMA on the MM cells, other studies excluded patients who didn’t meet a certain threshold level of BCMA expression, median lines of prior therapy differed, and conditioning regimens differed as well.

All trials, however, presented data on fewer than 20 patients.

“And so I think it’s a little too early to compare head-to-head between all of these, but they all are really demonstrating promising results so far,” he observed.

Toxicities

“Unfortunately, there’s no free lunch with CAR T cells,” Dr Cohen stated, “and these extraordinary responses do come at the cost of several somewhat unique toxicities that can be serious.”

Toxicities have included:

• Tumor lysis syndrome, which is expected and manageable
• B-cell aplasia, which is not as much of an issue with BCMA as with CD19-directed CAR Ts, since most B cells don’t express BCMA
• Hypogammaglobulinemia, which can be mitigated with IVIG
• CRS, which can be alleviated with tocilizumab
• Neurotoxicity and encephalopathy, which do not occur as frequently as CRS.

“These, I think, are things we still obviously need to learn more about and try to mitigate before this [BCMA-directed CAR therapy] is expanded and brought earlier to patients,” Dr Cohen said.

“The other issues with CAR T cells are logistical. Limited access (the procedure is available at only a few centers); manufacturing can take 2 to 4 weeks, during which time it is difficult to maintain disease control; and the cost is significant.”

“We are really in the early days of CAR cells for myeloma, but, certainly, this appears very bright in terms of its future.” 

* Data from the presentation differ from the abstract.