Sequential CD19- and Bcma-Specific Chimeric Antigen Receptor T Cell Treatment for RRMM: Report from a Single Center Study

Background: Relapsed and/or refractory multiple myeloma (RRMM) has a very poor prognosis, especially for chinese patients with limited therapeutic options. Chimeric antigen receptor transduced T cells (CARTs) had been approved to be one of the rescue strategies for malignant B cell hematological tumors. CARTs targeting B-Cell Maturation Antigen (BCMA) were effective against RRMM in recent published clinical studies. CD19 is expressed by B cells before terminal differentiation into plasma cells and is associated with the enhancement of tumor-propagating and drug-resistance properties of myeloma. Thus, CD19 is also a potential therapeutic target. To our knowledge, we firstly designed the clinical study to evaluate the safety and efficacy of sequential infusion of CD19 and BCMA-Specific CARTs for RRMM patients (pts) (NCT 03196414). Our initial results showed this stragety had substantial anti-myeloma activity and well tolerated toxicities, which had been released at the 59th ASH meeting. Here, we will report the latest clinical data of a total of 28 RRMM patients receiving combined autologous CARTs infusion.

Methods: Human T cells were collected from autologous peripheral blood mononuclear cells (PBSC). CART production was performed by the Unicar-Therapy Bio-medicine Technology Company (Shanghai, China). In this trial, RRMM pts firstly receive FC regimen as lymphodepleting conditioning , then were infused into CART-19 (1×10⁷/kg on day 0) and CART-BCMA (total dose range: 2-6.8×10⁷/kg) cells as split-dose infusions (40% on day 1 and 60% on day 2). After one month from CARTs infusion, some pts were adminstrated IMiDs for maintence therapy after hematopoietic recovery, including oral thalidomide 50mg/d or lenalidomide 10mg/d. This trial design and observation was seen in Blood,2017,130(Suppl.):506.The median follow-up time was 16 (3-28) months.

Results: By January 2019, 28 pts were enrolled in this clinical trial. Among them, 23 (82.1%) pts were males and 5 (17.9%) pts were females. The median age was 57.5 (range: 42-69) years old. All pts were resistant to proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), or both. These pts had received an average of 3 (2-8) lines of therapy prior to enrollment. The most common adverse event of CART therapy was acute cytokine release syndrome (CRS), which occurred in 28 pts (100%). 19 pts (67.9%) were evaluated grade 1-2 CRS. 7 pts (25.0%) were evaluated grade 3 CRS, and 2 pts (7.1%) were grade 4. High-grade CRS was associated with elevated levels of IL-6, IFNγ, IL-10 and CRP, especially IL-6 upgradation to thousands of times the baseline. Other toxicities within two weeks of CARTs infusion included fatigue (n=28; 100%), cytopenia (n=28; 100%), anemia (n=28; 100%), prolonged APTT (n=23; 82.1%), elevated creatinine (n=13; 46.4%), gastrointestinal reaction(n=9; 32.1%), elevated transaminase (n=9; 32.1%). Notably, one patient (CRS grade 4) developed grade 4 CRES who exhibited generalized seizure. But this life-threatening complication was quickly relieved after corticosteroids and sodium valproate administration. Two pts (7.1%) had HLH/MAS. No fatal or severe adverse events emerged after two weeks following the infusion. Chronic side effects included chronic diarrhea, hematocytopenia, mild infection, grade ≤2 bilirubin and/or transaminase elevation, hypogammaglobulinemia, etc. No treatment related mortality occurred in this group of pts.

Among the 28 pts who completed the CARTs infusion, 27 pts were monitored at predetermined time points and one patient lost follow-up. The overall response rate was 92.6%, and 88.9% of the pts were above PR. 11 pts (40.7%) were CR or sCR, 8 pts (29.6%) were VGPR, 5 pts (18.5%) were PR and one (3.7%) was MR. The remaining 2 pts, one (3.7%) was evaluated as SD and another (3.7%) was PD. 4 pts died from myeloma progression during the follow-up. Of those pts, the median PFS was 8 months. The median OS was 16 months.

Conclusions: Combined sequential administration of CART-19 and CART-BCMA cells can be manufactured from heavily-treated MM pts, and could elicit sustained remission for RRMM pts. Toxicities can be well tolerated. CARTs early expansion and persistence in vivo post infusion may be predictive of clinical outcome. How to prolong the survival time of CARTs in vivo is one of the subjects worth studying in the future.