CAR T-Cell Therapy UCARTCS1A Shows Early Activity in Relapsed/Refractory Myeloma

UCARTCS1A demonstrated early antitumor activity in heavily pretreated patients with relapsed/refractory multiple myeloma in whom previous CAR T-cell therapy and/or transplant had failed, according to preliminary data from the phase 1 MELANI-01 trial (NCT04142619) presented during the 2021 American Society of Gene and Cell Therapy Annual Meeting.¹

Expansion and persistence of UCARTCS1A was observed and was found to correlate with clinically meaningful antimyeloma activity and serum cytokine changes in very heavily pretreated patients with multiple myeloma. Also, the CAR T-cell product was noted to be detectable in patients, regardless of donor and batch.

“These preliminary data validate CS1 as a target for CAR T-cell products in multiple myeloma and that UCARTCS1A is a promising potential therapy for [those with this disease],” Krina K. Patel, MD, MSc, an associate professor of the Department of Lymphoma/Myeloma, Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center, said during a presentation on the results.

One of the benefits that comes with utilizing an allogeneic CAR T-cell approach over an autologous approach is that it affords the opportunity for off-the-shelf product availability, according to Patel. Patients are able to avoid a prolonged wait for the CAR T cells to be manufactured; the cells are able to be administered within a couple of weeks, Patel explained. In contrast, it can take 4 to 5 weeks to bring an autologous product to a treatment center.

Scalable manufacturing is another benefit of allogeneic approaches, and this can reduce costs and yield 100 or more doses from 1 batch of donor cells. Also, for allogeneic approaches, T cells are collected from healthy donors; these patients have not been given many steroids, chemotherapy, or have undergone autologous transplant. As such, their T cells will likely be more potent, Patel explained. Lastly, more flexible dosing is an option with allogeneic approaches; this allows for the possibility of redosing and alternate schedules.

UCARTCS1A is the first allogeneic CAR T-cell product developed to target CS1 and SLAMF7, both of which are highly and consistently expressed in multiple myeloma, according to Patel. The product knocks out the TRAC gene to avoid graft-versus-host disease through disruption of T-cell receptor (TCR) assembly. The product also knocks out CS1 to facilitate robust expansion and yield, while avoiding fratricide. Lastly, UCARTCS1A has a RQR8 safety switch, which is a CD20 mimotope that can use rituximab (Rituxan) to kill the cells, if necessary.

Previously, the CAR T-cell product demonstrated durable in vivo efficacy against MM1S tumors. Here, NSG mice were given a 5 x 10⁵ MM1S myeloma cell line, “which is known to be pretty aggressive,” Patel noted; this was labeled with GFP and was given for 10 days. Subsequently, the mice received the CAR T cells. Investigators observed CAR-positive cells at day 4 and M protein, which is a surrogate marker for multiple myeloma in mice and patients.

“We were able to see an early response, as well. However, eventually, the T cells went down, and the myeloma started to go back up,” Patel added. “Looking at the imaging, mice who [received] CAR T cells obviously did much better and lived longer and there was a dose-dependent response where the mice that got the higher dose did better, with a much longer survival.” Investigators were also able to demonstrate that the mice that received the CAR T-cell therapy experienced improvement in lytic lesions over time.

MELANI-01 enrolled patients with confirmed multiple myeloma per International Myeloma Working Group criteria who relapsed following previous therapy for their disease. To be eligible for enrollment, patients needed to have an ECOG performance status of 0 to 2 and acceptable organ function. They could have not previously received an investigational drug or cell/gene therapy targeting CS1.

“The key eligibility [for this trial] is similar to most cell therapy trials [that are done in] myeloma. However, for most of those trials, patients are not able to have previously received CAR T cells or BCMA-directed therapies,” Patel said. “In this trial, [those are not] ineligibility [criteria]. Our patients had really relapsed/refractory [disease.]”

After going through screening, patients received lymphodepletion chemotherapy that was comprised of fludarabine at a daily dose of 30 mg/m² for 3 days followed by cyclophosphamide at a daily dose of 1 g/m², also for 3 days. “The [cyclophosphamide] dose was 2 to 3 times higher than what [has been] used in most other trials,” Patel noted.

Patients then received treatment with UCARTCS1A. Patients were started at dose level 1, where they received 1 x 10⁶/kg. One patient went on to dose level 2, which was 3 x 10⁶/kg. Patients underwent their first disease evaluation at day 28.

The primary and secondary objectives of the study included safety and tolerability of UCARTCS1A, as well as determining the maximum-tolerated dose and efficacy of the product. Exploratory end points are examining expression of CS1 on multiple myeloma cells, UCARTCS1A expansion and persistence, and changes in serum biomarkers or immune cell reconstitution.

Patel shared information on 5 patients who received treatment with UCARTCS1A to date; 4 of the patients received dose level 1 (102-101, 102-109, 102-107, and 102-111) and 1 patient (102-113) received dose level 2.

Four of the 5 patients (102-101, 102-109, 102-107, and 102-113) had previously received over 11 lines of therapy and had most had previously received a BCMA-directed therapy. “Just to put this into context, most of the autologous CAR T-cell trials that are done have patients who had a median of 5 to 6 prior lines of treatment,” Patel noted.

One patient (102-111) had received only 4 prior lines of therapy and was the only patient who had cells expand and responded on dose level 1. However, the patient had very high-risk disease with 90% plasma cells. “He had the most myeloma going into the trial,” Patel said.

Notably, patient 102-113 who had received dose level 2 and also experienced an expansion of cells at day 7 had received 13 prior lines of therapy, including 2 prior BCMA-targeted CAR T-cell therapies, the last of which was administered just 5 months prior to the study.

Patient 102-111 was 55 years of age, had 4 prior lines of therapy and 90% of bone marrow involvement. He had relapsed within 6 months of every prior line of therapy and he never experienced more than a partial response (PR) to any of his prior treatments, according to Patel. When looking at his peripheral blood at day 28, investigators noted that the CD45+ CAR-positive lymphocytes was almost 72% and a subgroup of CD8+ effector cells that are TCRαβ–negative CAR-positive cells, were about 46%.

“[Some might] think that allogenic cells would not last very long, but for this patient, we definitely saw the majority of T cells still there that were CAR positive,” Patel said. “For him, we were able to get a bone marrow [sample] at month 3, where we could also see CD45+ CAR-positive cells at 60% in the bone marrow of all CD45+ cells. The CD8+ effector [cells] were at 92%.”

Moreover, CAR-positive cells were observed in the patient’s peripheral blood starting at day 14; they peaked at day 21, and then started to decrease. However, some of these cells were still observed at day 80 to 86, according to Patel. The patient’s white blood cell count was low, while peripheral blood was high, until approximately day 28, before it started decreasing. However, the patient’s bone marrow remained high, even at day 77, in terms of the vector copy number of the CAR T cells.

This patient experienced grade 2 cytokine release syndrome (CRS) within the first week of cell infusion. The patient also developed hemophagocytic lymphohistiocytosis (HLH), which has previously been observed with other autologous CAR T-cell products in multiple myeloma. Investigators treated the patients with anakinra (Kineret), dexamethasone, etoposide, and the rituximab kill switch. The rationale for triggering the kill switch was because the patient had reactivation of HHV6, which developed into HHV6 encephalitis.

“Per the FDA, we were monitoring HHV6 and HHV7 levels, as we do for most of our CAR T-cell therapy trials. We were monitoring this [and when his levels were high enough that we decided to treat], the patient got admitted for antivirals, improved, went home, and then came back with an encephalitis picture. Initially, we treated him dexamethasone and gave the rituximab kill switch thinking that if it was immune effector cell-associated neurotoxicity, we could kill off some of the cells. But in the end, it was HHV6 encephalitis.”

Although the patient did improve, and he had double antiviral coverage, he eventually passed away on day 109 from organizing pneumonia in the context of prolonged lymphopenia in the absence of multiple myeloma progression.

“At the time, he did not have any myeloma and he had [experienced] this response that he had never had before, a near complete response” Patel explained. “We looked at his bone marrow, which was minimal residual disease–negative at the 10-5 level. However, because of the prolonged lymphopenia, he ended up with this infection.”

Multiple factors may have contributed to the prolonged lymphopenia, including viral reactivation, concomitant antivirals, and recent prior stem cell transplant, Patel explained.

The other patient with expansion, patient 102-113, was observed to have 25% CD45+ CAR-positive lymphocytes in the peripheral blood at day 9, 77% of which were CD8+ effector cells, according to Patel. Notably, investigators were unable to collect a bone marrow sample from the patient. In the peripheral blood, investigators observed expansion at day 7 and then a peak, and then the vector copy number persisted over the time the blood samples were obtained.

This patient had previously received 14 lines of therapy, including 2 previous BCMA-directed CAR T-cell therapies and associated lymphodepleting regimens, autologous transplant, and venetoclax (Venclexta), as his last line of therapy. “The patient did not have any options left and we saw this fantastic response, where the lambda light chains had gone done by almost 90%; his M protein had at least a PR by just day 14.

However, this patient had CRS and HLH, as well. “We treated him with etoposide, anakinra, dexamethasone, and the rituximab kill switch and he had improvement in his platelet and his liver function tests,” Patel added. “The HLH clinically improved for him. However, at day 25, he passed away.”

An autopsy revealed G5 hemorrhagic pancreatitis, although he had not exhibited any clinical signs of this condition during his hospital stay. Investigators also found disseminated mucormycosis and pseudomonal pneumonia.

Select serum cytokine changes over time were found to correlate with expansion of the CAR T-cell product. “Cytokines were increased much more in the patients who expanded vs those who did not expand at all,” Patel noted.

MELANI-01 is currently enrolling patients with protocol modifications, including restarting at dose level -1 (3 x 105). Moreover, lower doses of lymphodepleting chemotherapy are being administered now in an attempt to address lymphopenia and lead to added expansion. The trial will also have additional requirements for monitoring and managing patients with regard to opportunistic infections, as well as CRS and HLH.

Reference

Patel KK, Bharathan M, Siegel D, et al. UCARTCS1A, an allogeneic CAR T-cell therapy targeting CS1 in patients with relapsed/refractory multiple myeloma (RRMM): preliminary translational results from a first-in-human phase I trial (MELANI-01). 2021 American Society of Gene and Cell Therapy Annual Meeting; May 11-14, 2021; Virtual. Accessed May 13, 2021. Abstract 118.