Adoptive Immunotherapy beyond CAR T-Cells

Abstract

Adoptive cell immunotherapy (ACT) is a vibrant field of cancer treatment that began progressive development in the 1980s. One of the most prominent and promising examples is chimeric antigen receptor (CAR) T-cell immunotherapy for the treatment of B-cell hematologic malignancies. Despite success in the treatment of B-cell lymphomas and leukemia, CAR T-cell therapy remains mostly ineffective for solid tumors. This is due to several reasons, such as the heterogeneity of the cellular composition in solid tumors, the need for directed migration and penetration of CAR T-cells against the pressure gradient in the tumor stroma, and the immunosuppressive microenvironment. To substantially improve the clinical efficacy of ACT against solid tumors, researchers might need to look closer into recent developments in the other branches of adoptive immunotherapy, both traditional and innovative. In this review, we describe the variety of adoptive cell therapies beyond CAR T-cell technology, i.e., exploitation of alternative cell sources with a high therapeutic potential against solid tumors (e.g., CAR M-cells) or aiming to be universal allogeneic (e.g., CAR NK-cells, γδ T-cells), tumor-infiltrating lymphocytes (TILs), and transgenic T-cell receptor (TCR) T-cell immunotherapies. In addition, we discuss the strategies for selection and validation of neoantigens to achieve efficiency and safety. We provide an overview of non-conventional TCRs and CARs, and address the problem of mispairing between the cognate and transgenic TCRs. Finally, we summarize existing and emerging approaches for manufacturing of the therapeutic cell products in traditional, semi-automated and fully automated Point-of-Care (PoC) systems.

Keywords: CAR NK-cell; CAR T-cell; TIL; chimeric antigen receptor; neoantigen; neoepitope; peptide; transgeneic TCR.

Figure 1

The diverse nature of adoptive immunotherapy. Infusion of tumor infiltrating lymphocytes (TILs) is one of the oldest clinical approaches in T-cell-based immunotherapy. The isolated TILs are expanded ex vivo and infused back to the patient. In addition, TILs and other T-cells may be used for isolation of T-cell receptors (TCRs) for further genetic engineering and generation of transgenic TCR therapies. Alternatively, to widespread CAR T-cells, other cell populations (e.g., NK-cells, macrophages) may be transduced to produce CAR NK-cells and CAR M-cells, respectively. Cellular therapies that are primarily applied for the treatment of solid tumors (*) or hematological malignancies (+).

Figure 2

The structure of TCR α and β chains. The TCR constant domains are responsible for the correct complex assembly and binding to CD3 chains, whereas the variable domains are involved in recognition of the peptide–MHC complex. Complementary Determining Regions 3 of α (CDR3α) and β (CDR3β) chains are assembled during somatic mutagenesis and V(D)J recombination and are the most important for antigen recognition. The other CDRs (V-gene specific) are germline encoded and contribute to peptide–MHC recognition.

Figure 3

The strategies for neoantigen discovery. (1) A laborious approach that includes: (a) tumor genome and RNA sequencing; followed by (b) MS analysis of the immunopeptidome (peptides dissociated from peptide–MHC complex) and (c) mapping of these peptides to the source genome/transcriptome. (2) Analysis of the sequencing data allows computational prediction of putative HLA-binding peptides by NetMHCPan, SYFPEITHI, or HLAthena algorithms. (3) Novel approaches for epitope screening based on human genome-wide libraries. Approaches 1 and 2 require subsequent validation to confirm correct processing and presentation of the identified peptides (for approach 2), as well as their potential immunogenicity (for both approaches). The validation step includes ex vivo expansion of T-cells in presence of peptide- or minigene-pulsed dendritic cells (DCs) or using approach 3.

Figure 4

Addressing mispairing issues. The top semicircle (rose) depicts modifications of transgenic TCRs that facilitate correct pairing of ɑ and β chains. The bottom semicircle (green) outlines regulation of the endogenous TCR expression.

Figure 5

The differences and similarities in the design of transgenic receptors for adoptive immunotherapy.

Figure 6

Evolution of the bioreactor platforms. The most advanced systems include G-Rex^® by Wilson Wolf, Z^®RP by Zellwerk, Xuri^® (WAVE^®) by Cytiva, CliniMACS Prodigy^® by Miltenyi Biotec, Cocoon^® by Lonza (Basel, Switzerland), and Quantum^® by Terumo (Tokyo, Japan).