ASH13 just around the corner – quick update of CAR-T technology

December 2, 2013.
by Paul D Rennert 

Part 7. Chimeric Antigen Receptor T cell technology (CAR-T) in the treatment of hematopoietic malignancies.

The American Society of Hematology Meeting will take place in New Orleans, December 7 – 10, 2013. The abstracts are available at http://www.hematology.org/Meetings/Annual-Meeting/Abstracts/5810.aspx
Having detoured briefly into myelofibrosis (see parts 6a and b), there are just a few more subjects to try to cover this week. With luck and time, I’ll get through this bit today and then maybe on to lymphoma genetics, we’ll see.
This is from the introduction to Carl June’s seminal 2011 NEJM case report:
“We designed a lentiviral vector expressing a chimeric antigen receptor with specificity for the B-cell antigen CD19, coupled with CD137 … (4-1BB) and CD3-zeta … signaling domains. A low dose (approximately 1.5×10^5 cells per kilogram of body weight) of autologous chimeric antigen receptor–modified T cells reinfused into a patient with refractory … CLL expanded to a level that was more than 1000 times as high as the initial engraftment level in vivo, with delayed development of the tumor lysis syndrome and with complete remission. Apart from the tumor lysis syndrome, the only other grade 3/4 toxic effect related to chimeric antigen receptor T cells was lymphopenia.” (Porter et al. 2011. NEJM 365: 725-733). The therapy induced long term remission is a patient who had failed 4 rounds of rituximab+chemo, and then had failed alemtuzumab, anti-CD52, therapy. Pretty amazing.
The anti-CD19 CAR is essentially an antibody fragment containing a single chain Fv (antigen binding domain). The CD3-zeta chain induces T cell activation and the addition of the 4-1BB cytoplasmic domain ensures prolonged and robust response – 4-1BB is in immune checkpoint activator, and is gaining some favor in its own right in immunotherapy, through the development of agonist anti-4-1BB antibodies. The CAR-T components are introduced to the patient’s own T cells ex vivo via lentivirus transduction, then given back to the patient in hopes of inducing a T cell mediated immune response to the cancer (e.g. a CD19+ CLL). The original case reports were followed for up to 3 years, as reported in Abstract #4162. Of 14 patients treated in the pilot studies, the ORR = 57% (21% CR and 30% PR). 43% of patients did not respond. Of the PR cohort, 40% progressed within 4 months. So that’s about 1/3 of patients with a durable response.
Additional clinical trials have been funded via collaboration with Novartis, who has bought the technology and patents. A few of these are updated at ASH. The CLL and ALL data for patients treated with the anti-CD19 CAR T cells (CTL019) are summarized in Abstract #163. 24 rrCLL patients have been treated using 2 different protocols that vary by the number of CTL019 cells given back to the patient. The response rates were CR = 21%, PR = 29% (so ORR = 50%) and non-responders = 50%. In pediatric ALL (n=14) the CR = 57%; the rest of the patients (43%) either did not respond or progressed. In adult ALL, all 3 patients had a CR (=100%). CRs were always accompanied by in vivo expansion and persistence of CTL019 cells. Tumor cells were eliminated from circulation and also, importantly, from bone marrow. Molecular analyses showed that tumor cells were essentially eliminated in patients with CR – this is defined as minimal residual disease (i.e. not detectable). Additional data specific to these studies are reported in Abstract #873 (CLL) and Abstract #67 (ALL) – the latter study reports persistence up to 15 months. Another group at U Penn reported similarly high RRs in ALL. Lee et al (Abstract #68) report the use of an CD19-CD28-CD3zeta CAR construct to engineer t cells for use in ALL, with an initial CR (n=7) of 71.5%, with other 2 PR responders and 2 non-responders. These are impressive early data from multiple studies.
Steve Rosenberg’s group is also reporting use of anti-CD19 CAR-T cells, these made using a gamma-retrovirus construct to genetically modify the T cells. The technology differs also by use of the CD28 signaling domain instead of 4-1BB, along with CD3-zeta. Of 14 patients with rrCLL, rrDLBCL or primary mediastinal BCL, 36% achieved a CR and 43% a PR, the rest being non-responders or SD. All responders (PR + CR = 79%) were ongoing at the time of abstract submission. The study will be further updated at the meeting. The trial was funded under a CRADA-based collaboration between the NCI and Kite Pharma, a private biotech company.
Given the compelling response rates observed, it is unclear whether the ex vivo selection and expansion methods employed by the MD Anderson group will add benefit. Laurence Cooper and colleagues will present a CD19 CAR technique that utilizes artificial antigen-presenting cells to select the T cell population that is then given following hematopoietic stem cell transplantation in ALL and NHL patients (Abstracts #166 and #4208). Their very early results will be updated at the meeting. Additional efforts targeting CD19 include the trial in rrCLL patients who have received only 1 prior chemotherapy regimen; the idea is that these patients are earlier in the disease course and may have better response rates. It is not possible to tell from the Abstract (#874) if this effort is succeeding, but an update is promised at the meeting.
Turning from the CD19-directed technologies, Carl June’s group is presenting the first clinical data on the use of engineered T cells in multiple myeloma. The T cells are expanded using CD3/CD28 beads (a technology I worked on 20 years ago at Repligen, in the context of HIV therapy) and are engineered to express a modified TCR that recognizes the MM antigens NY-ESO-1/LAGE1. The recognition of this peptide complex is HLA-class restricted, so the patients are screened in advance for responsive HLA haplotypes. The T cells are infused followed depletion and stem cell transplantation, so CAR-T is used here in the context of adjunct therapy. Best response ORR = 100%, although some patients have since progressed. An update will be given at the meeting. Also of note is a trial in which this novel CAR-T therapy is used in a non-transplant setting (no data available yet). An interesting twist is the use of kappa-light chain of surface immunoglobulin expressed on malignant B cells (as opposed to lambda light chain expressed by most normal B cells? – I guess that’s right). A group from Baylor, funded by Celgene, will present Phase 1 data (Abstract #506). Another CAR antigen technology in preclinical development at U Penn targets CD123 for AML (Abstract #143). Preclinical data from the OSU group show that a different MM antigen can be used in the CAR-T setting. Abstract #14 shows that a CS-1 directed CAR works in a mouse xenograft model. I like the straightforward description of the technology: “We successfully generated a specific CS1-CAR construct with a lentiviral vector backbone, sequentially containing a signal peptide (SP), a heavy chain variable region (VH), a linker, a light chain variable region (VL), a hinge, CD28 and CD3epsilon.” Simple, right? Finally, Haso et al from the NIH compare CD22-targeting CAR constructs using different signaling chains (4-1BB v CD28) in preclinical mouse models of ALL, and report superior results using the 4-1BB construct (Abstract #1431). This is nice as they used a humanized mouse model, the NOD/SCID/Common gamma chain KO mouse (NSG), engrafted with a human ALL line. Love the humanized mouse technology, right up my alley.

A persistent theme in the evolving treatment of leukemias and lymphomas is the use of combination therapies. We see a similar trend developing with CAR-T technologies. Paolo Ghia et al combine a CAR directed to CD23 along with low dose lenalidomide treatment using the Rag2/Common gamma chain KO humanized mouse model and cell from CLL patients – nice work (Abstract #4171). A second study evaluated the use of mTOR modulation in the context of CAR-T therapy (Abstract #4488). As this technology continues to advance we can expect to see additional uses of targeted or other therapies in combination.