T cells expressing chimeric antigen receptors can cause anaphylaxis in humans

Abstract

T cells can be redirected to overcome tolerance to cancer by engineering with integrating vectors to express a chimeric antigen receptor (CAR). In preclinical models, we have previously shown that transfection of T cells with mRNA coding for a CAR is an alternative strategy that has antitumor efficacy and the potential to evaluate the on-target off-tumor toxicity of new CAR targets safely due to transient mRNA CAR expression. Here, we report the safety observed in four patients treated with autologous T cells that had been electroporated with mRNA coding for a CAR derived from a murine antibody to human mesothelin. Because of the transient nature of CAR expression on the T cells, subjects in the clinical study were given repeated infusions of the CAR-T cells to assess their safety. One subject developed anaphylaxis and cardiac arrest within minutes of completing the third infusion. Although human anti-mouse immunoglobulin (Ig)G antibodies have been known to develop with CAR-transduced T cells, they have been thought to have no adverse clinical consequences. This is the first description of clinical anaphylaxis resulting from CAR-modified T cells, most likely through IgE antibodies specific to the CAR. These results indicate that the potential immunogenicity of CARs derived from murine antibodies may be a safety issue for mRNA CARs, especially when administered using an intermittent dosing schedule.

Trial registration: ClinicalTrials.gov NCT01355965.

Figure 1. Clinical trial schema

The subject was originally enrolled onto cohort 1, where 10⁸ meso-RNA-CART cells were administered on Day 0 and 10⁹ meso RNA CART cells were administered on Day 7. Safety assessments were performed between days 0 and 7, and repeat staging was performed by CT scan on day 35. The subject was then enrolled into an extended cohort to receive an additional 6 doses of T cells that were scheduled for Monday/Wednesday/Friday for two weeks. However, the subject developed anaphylaxis immediately after the 3^rd infusion (i.e. the first of Extended Cohort 1), and therefore, did not receive any further infusions (marked with an ‘X’).

Figure 2

Serum tryptase in blood. Peripheral blood serum samples at baseline and several time points after the SAE were analyzed for levels of serum tryptase. The dashed line indicates the upper limit of normal range (0.4 – 10.9 μg/L).

Figure 3

(A) Serum cytokines. Peripheral blood serum samples obtained at baseline and from several time points after the event were analyzed for levels of 30 cytokines. Only cytokines elevated at least 1.5-fold over baseline are shown. IL-6 levels at 1 hour after infusion were above the limit of quantification of the assay. (B) Pleural fluid cytokines. The subject had a pleurex catheter in place and pleural fluid was collected 24 hours after the event and periodically thereafter. The levels of 30 cytokines were measured but only the four that were elevated at least 1.5-fold above baseline are shown. IL-6 levels 24 hours after the event were above the limit of quantification of the assay.