Profiling of donor-specific immune effector signatures in response to rituximab in a human whole blood loop assay using blood from CLL patients

Rituximab is widely used in the treatment of haematological malignancies, including chronic lymphocytic leukaemia (CLL), the most common leukaemia in adults. However, some patients, especially those with high tumour burden, develop cytokine release syndrome (CRS). It is likely that more patients will develop therapy-linked CRS in the future due to the implementation of other immunotherapies, such as CAR T-cell, for many malignancies. Current methods for CRS risk assessment are limited, hence there is a need to develop new methods. To better recapitulate an in vivo setting, we implemented a unique human whole blood "loop" system to study patient-specific immune responses to rituximab in blood derived from CLL patients. Upon rituximab infusion, both complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) profiles were evident in CLL patient blood, coincident with CLL cell depletion. Whereas B cell depletion is induced in healthy persons in the blood loop, only patients display B cell depletion coupled with CRS. With the exception of one donor who lacked NK cells, all other five patients displayed variable B cell depletion along with CRS profile. Additionally, inhibition of CDC or ADCC via either inhibitors or antibody Fc modification resulted in skewing of the immune killing mechanism consistent with published literature. Herein we have shown that the human whole blood loop model can be applied using blood from a specific indication to build a disease-specific CRS and immune activation profiling ex vivo system. Other therapeutic antibodies used for other indications may benefit from antibody characterization in a similar setting.

Melanoma cells can be eliminated by sialylated CD43 × CD3 bispecific T cell engager formats in vitro and in vivo

Targeted cancer therapy with monoclonal antibodies has proven successful for different cancer types but is limited by the availability of suitable antibody targets. CD43s, a unique sialylated form of CD43 expressed by hematologic malignancies, is a recently identified target and antibodies interacting with CD43s may have therapeutic potential against acute myeloid leukemia (AML) and myelodysplastic syndrome. CD43s is recognized by the human antibody AT1413, that was derived from a high-risk AML patient who successfully cleared leukemia after allogeneic stem cell transplantation. Here we observed that AT1413 binds also to certain non-hematopoietic tumor cells, particularly melanoma and breast cancer. AT1413 immune precipitated CD43s from melanoma cells confirming that it recognizes the same target on melanoma as on AML. AT1413 induced antibody-dependent cellular cytotoxicity against short-term cultured patient-derived melanoma samples. However, AT1413 was unable to affect the growth of melanoma cells in vivo. To increase the efficacy of AT1413 as a therapeutic antibody, we generated two different formats of bispecific T-cell engaging antibodies (TCEs): one binding bivalently (bTCE) and the other monovalently (knob-in-hole; KiH) to both CD43s and CD3ε. In vitro, these TCEs redirected T-cell cytotoxicity against melanoma cells with differences in potencies. To investigate their effects in vivo, we grafted mice that harbor a human immune system with the melanoma cell line A375. Treatment with both AT1413 bTCE and AT1413 KiH significantly reduced tumor outgrowth in these mice. These data indicate a broad therapeutic potential of AT1413 that includes AML and CD43s-expressing solid tumors that originate from CD43-negative tissues.

A phase II study of antibody-drug conjugate, TAK-264 (MLN0264) in previously treated patients with advanced or metastatic pancreatic adenocarcinoma expressing guanylyl cyclase C

Background This phase II open-label, multicenter study evaluated the efficacy, safety, and tolerability of TAK-264 in previously treated patients with advanced or metastatic pancreatic adenocarcinoma expressing guanylyl cyclase C (GCC). Methods Patients with advanced or metastatic pancreatic adenocarcinoma expressing GCC (H-score ≥ 10) received TAK-264 1.8 mg/kg on day 1 of a 21-day cycle as a 30-min intravenous infusion for up to 1 year or until disease progression or unacceptable toxicity. The primary objective was overall response rate (ORR [complete response + partial response (PR)]). Secondary objectives included evaluations of the safety and pharmacokinetic profile of TAK-264 (NCT02202785). Results 43 patients were enrolled and treated with 1.8 mg/kg TAK-264: 11, 15, and 17 patients with low, intermediate, and high GCC expression, respectively. Median number of treatment cycles received was two (range 1-10). The ORR was 3%, including one patient with intermediate GCC expression who achieved a PR. All patients experienced ≥1 adverse events (AE). The majority of patients experienced grade 1/2 AEs affecting the gastrointestinal tract. Fifteen (35%) patients experienced ≥grade 3 drug-related AEs; five (12%) patients had a serious AE. The most common (≥10% of patients) all-grade drug-related AEs were nausea (33%), fatigue (28%), neutropenia (23%), decreased appetite (23%), vomiting (16%), asthenia (16%), and alopecia (14%). Conclusions TAK-264 demonstrated a manageable safety profile; however, the low efficacy of TAK-264 observed in this study did not support further clinical investigation.