Enhancement of lytic activity of leukemic cells by CD8+ cytotoxic T lymphocytes generated against a WT1 peptide analogue

A cell-engineered system to assess tumor cell sensitivity to CD8+ T cell-mediated cytotoxicity

In vitro assays that evaluate CD8+ T cell-mediated cytotoxicity are important to aid in the development of novel therapeutic approaches to enhance anti-tumor immune responses. Here, we describe a novel cytotoxicity co-culture assay that circumvents the problem of highly variable allogeneic responses and obviates the constraints of HLA-restriction between effector and target cells. We show that this assay can be easily applied to a panel of tumor cell lines to provide additional insights into intrinsic drivers of sensitivity/resistance to T cell-mediated killing, and to evaluate the impact of targeted therapies on both tumor and T cell compartments.

Understanding CD8+ T-cell responses toward the native and alternate HLA-A*02:01-restricted WT1 epitope

The Wilms' tumor 1 (WT1) antigen is expressed in solid and hematological malignancies, but not healthy tissues, making it a promising target for cancer immunotherapies. Immunodominant WT1 epitopes, the native HLA-A2/WT1_126-134 (RMFPNAPYL) (HLA-A2/RMFPNAPYL epitope (WT1A)) and its modified variant YMFPNAPYL (HLA-A2/YMFPNAPYL epitope (WT1B)), can induce WT1-specific CD8⁺ T cells, although WT1B is more stably bound to HLA-A*02:01. Here, to further determine the benefits of those two targets, we assessed the naive precursor frequencies; immunogenicity and cross-reactivity of CD8⁺ T cells directed toward these two WT1 epitopes. Ex vivo naive WT1A- and WT1B-specific CD8⁺ T cells were detected in healthy HLA-A*02:01⁺ individuals with comparable precursor frequencies (1 in 10⁵–10⁶) to other naive CD8⁺ T-cell pools (for example, A2/HIV-Gag_77-85), but as expected, ~100 × lower than those found in memory populations (influenza, A2/M1_58-66; EBV, A2/BMLF1_280-288). Importantly, only WT1A-specific naive precursors were detected in HLA-A2.1 mice. To further assess the immunogenicity and recruitment of CD8⁺ T cells responding to WT1A and WT1B, we immunized HLA-A2.1 mice with either peptide. WT1A immunization elicited numerically higher CD8⁺ T-cell responses to the native tumor epitope following re-stimulation, although both regimens produced functionally similar responses toward WT1A via cytokine analysis and CD107a expression. Interestingly, however, WT1B immunization generated cross-reactive CD8⁺ T-cell responses to WT1A and could be further expanded by WT1A peptide revealing two distinct populations of single- and cross-reactive WT1A⁺CD8⁺ T cells with unique T-cell receptor-αβ gene signatures. Therefore, although both epitopes are immunogenic, the clinical benefits of WT1B vaccination remains debatable and perhaps both peptides may have separate clinical benefits as treatment targets.

Role of T cell receptor affinity in the efficacy and specificity of adoptive T cell therapies

Over the last several years, there has been considerable progress in the treatment of cancer using gene modified adoptive T cell therapies. Two approaches have been used, one involving the introduction of a conventional αβ T cell receptor (TCR) against a pepMHC cancer antigen, and the second involving introduction of a chimeric antigen receptor (CAR) consisting of a single-chain antibody as an Fv fragment linked to transmembrane and signaling domains. In this review, we focus on one aspect of TCR-mediated adoptive T cell therapies, the impact of the affinity of the αβ TCR for the pepMHC cancer antigen on both efficacy and specificity. We discuss the advantages of higher-affinity TCRs in mediating potent activity of CD4 T cells. This is balanced with the potential disadvantage of higher-affinity TCRs in mediating greater self-reactivity against a wider range of structurally similar antigenic peptides, especially in synergy with the CD8 co-receptor. Both TCR affinity and target selection will influence potential safety issues. We suggest pre-clinical strategies that might be used to examine each TCR for possible on-target and off-target side effects due to self-reactivities, and to adjust TCR affinities accordingly.

Integration of epidemiology, immunobiology, and translational research for brain tumors

We recently identified a pivotal role for the host type I interferon (IFN) pathway in immunosurveillance against de novo mouse glioma development, especially through the regulation of immature myeloid cells (IMCs) in the glioma microenvironment. The present paper summarizes our published work in a number of areas. We have identified single-nucleotide polymorphisms (SNPs) in human IFN genes that dictate altered prognosis of patients with glioma. One of these SNPs (rs12553612) is located in the promoter of IFNA8 and influences its activity. Conversely, recent epidemiologic data show that chronic use of nonsteroidal anti-inflammatory drugs lowers the risk of glioma. We translated these findings back to our de novo glioma model and found that cyclooxygenase-2 inhibition enhances antiglioma immunosurveillance by reducing glioma-associated IMCs. Taken together, these findings suggest that alterations in myeloid cell function condition the brain for glioma development. Finally, in preliminary work, we have begun applying novel immunotherapeutic approaches to patients with low-grade glioma with the aim of preventing malignant transformation. Future research will hopefully better integrate epidemiological, immunobiological, and translational techniques to develop novel, preventive approaches for malignant gliomas.

What T cells see in WT-1

The Wilms tumor protein, WT-1, is a widely recognized tumor antigen that is aberrantly expressed in myeloid and lymphoid leukemia and in this issue of Blood, Doubrovina et al report the most extensive catalog heretofore of HLA-restricted immunogenic peptides derived from WT-1, which are recognized by CD8 and CD4T cells.

Identification of a novel peptide derived from the M-phase phosphoprotein 11 (MPP11) leukemic antigen recognized by human CD8+ cytotoxic T lymphocytes

BACKGROUND AND OBJECTIVES

There is an urgent need for the development of leukemia-targeted immunotherapeutic approaches using defined leukemia-associated antigens that are preferentially expressed by most leukemia subtypes and absent or minimally expressed in vital tissues. M-phase phosphoprotein 11 protein (MPP11) is extensively overexpressed in leukemic cells and therefore is considered an attractive target for leukemia T cell therapy. We sought to identify potential CD8+ cytotoxic T lymphocytes that specifically recognised peptides derived from the MPP11 antigen.

METHODS

A computer-based epitope prediction program SYFPEITHI, was used to predict peptides from the MPP11 protein that bind to the most common HLA- A*0201 molecule. Peptide binding capacity to the HLA-A*0201 molecule was measured using the T2 TAP-deficient, HLA-A*0201-positive cell line. Dendritic cells were pulsed with peptides and then used to generate CD8+ cytotoxic T lymphocytes (CTL). The CML leukemic cell line K562-A2.1 naturally expressing the MPP11 antigen and engineered to express the HLA-A*0201 molecule was used as the target cell.

RESULTS

We have identified a potential HLA-A*0201 binding epitope (STLCQVEPV) named MPP-4 derived from the MPP11 protein which was used to generate a CTL line. Interestingly, this CTL line specifically recognized peptide-loaded target cells in both ELISPOT and cytotoxic assays. Importantly, this CTL line exerted a cytotoxic effect towards the CML leukemic cell line K562-A2.1.

CONCLUSION

This is the first study to describe a novel epitope derived from the MPP11 antigen that has been recognized by human CD8+ CTL.

Structures of native and affinity-enhanced WT1 epitopes bound to HLA-A*0201: implications for WT1-based cancer therapeutics

Presentation of peptides by class I or class II major histocompatibility complex (MHC) molecules is required for the initiation and propagation of a T cell-mediated immune response. Peptides from the Wilms Tumor 1 transcription factor (WT1), upregulated in many hematopoetic and solid tumors, can be recognized by T cells and numerous efforts are underway to engineer WT1-based cancer vaccines. Here we determined the structures of the class I MHC molecule HLA-A*0201 bound to the native 126-134 epitope of the WT1 peptide and a recently described variant (R1Y) with improved MHC binding. The R1Y variant, a potential vaccine candidate, alters the positions of MHC charged side chains near the peptide N-terminus and significantly reduces the peptide/MHC electrostatic surface potential. These alterations indicate that the R1Y variant is an imperfect mimic of the native WT1 peptide, and suggest caution in its use as a therapeutic vaccine. Stability measurements revealed how the R1Y substitution enhances MHC binding affinity, and together with the structures suggest a strategy for engineering WT1 variants with improved MHC binding that retain the structural features of the native peptide/MHC complex.