CD58 Aberrations Limit Durable Responses to CD19 CAR in Large B Cell Lymphoma Patients Treated with Axicabtagene Ciloleucel but Can be Overcome through Novel CAR Engineering

CD19 CAR T cells have revolutionized the treatment of relapsed and refractory (R/R) large B cell lymphomas (LBCL), mediating durable complete responses in approximately 40-50% of patients. Besides a loss or decrease in CD19 expression, no studies have identified tumor specific factors driving inherent or acquired resistance to CAR T cells in LBCL. Mutations in and loss of expression of LFA-3 (CD58) have been described in approximately 20% of cases of LBCL. As the ligand for CD2 on T cells, CD58 provides costimulation to T cells and CD58 loss or mutation has been linked to immune resistance in LBCL.

We evaluated CD58 status in fifty-one R/R LBCL patients treated at Stanford with commercial axicabtagene ciloleucel (axi-cel) through immunohistochemistry (IHC) on tumor biopsy samples and/or deep sequencing of circulating tumor DNA by CAPP-Seq. We identified 12/51 (24%) patients with a CD58 aberration (lack of expression by IHC or mutation by CAPP-Seq). Progression-free survival (PFS) was significantly decreased in patients with a CD58 aberration (median PFS for CD58 aberration 3 months vs. not reached for CD58 intact, p<0.0001). In fact, only 1/12 patients with a CD58 alteration achieved a durable, complete response to axi-cel, while the remaining 11 patients progressed, most commonly after a period of initial response. Partial responses were more common among patients with CD58 aberrations (58% for CD58 aberration vs 10% for CD58 intact, p<0.001), and complete responses were less common (25% for CD58 aberration vs 82% for CD58 intact, p<0.0001).

To probe the biology of CAR T cell responses towards tumors lacking functional CD58, we generated a CD58 knockout Nalm6 model. CD19.CD28.ζ, CD19.4-1BB.ζ, and CD22.4-1BB.ζ CAR T cells demonstrated significantly reduced cytokine production and cytolytic activity in response to CD58 KO vs wildtype (WT) tumor cells. Additionally, while mice inoculated with WT Nalm6 and treated with any of the three CARs demonstrate complete responses and prolonged leukemia-free survival, mice inoculated with CD58KO Nalm6 demonstrated only partial responses, eventual tumor progression, and death from leukemia.

CD2, the T cell ligand for CD58, plays both an adhesive role and a costimulatory role in T cells. CD2 knockout resulted in significantly reduced cytokine production after CAR stimulation. Re-expression of only the CD2 extracellular domain did not rescue CAR function, indicating that CD2 signaling is essential for full CAR activation. Additionally, when we stimulated CD19 CAR T cells with anti-idiotype antibody (CAR stimulation), soluble CD58 (CD2 stimulation), or both, we observed significantly enhanced phosphorylation of both CD3ζ and ERK by western blot in CAR T cells stimulated through both the CAR and CD2. Phosphorylation analysis by mass spectrometry revealed that CD2 stimulation enhances phosphorylation of proximal signaling molecules in the TCR pathway (LCK, LAT, CD3ε among others) and also mediators of actin-cytoskeletal rearrangement in CAR T cells, consistent with effects in natural T cell responses.

To overcome CD58 loss in LBCL, we generated second- and third-generation CAR T cell constructs integrating CD2 costimulatory domains within the CAR molecule. While these cis constructs demonstrated increased potency against CD58KO cells in vitro, they were unable to ultimately overcome CD58 loss in vivo. However, when CARs were co-expressed with an additional CD2 receptor in trans, they mediated significant anti-tumor activity in vivo, overcoming CD58 knockout in tumor cells.

In conclusion, we have identified that CD58 status is an important biomarker for durable response to CAR T cells in LBCL. We modeled the biologic basis for this finding and generated CAR T cells capable of overcoming CD58 loss in B cell malignancies. CD58 mutations have been reported in many cancers, including multiple myeloma and colon cancer, and are likely to play a role in immune evasion for CAR T cells as they are developed for additional histologies. These data provide rationale for investigating CD58 status for patients receiving CAR based therapeutics and devising next generation CARs capable of overcoming this newly discovered mechanism of resistance.