An immunotherapy antibody targeting CD4 T-cells anergy in HIV and cancer
CD4 T lymphocytes are white blood cells that act as the conductors of the immune response. Most of them are valuable aides to both innate (the body's first line of defense) and adaptive immune cells (the memory immunity cells that underpin vaccination). CD4 T lymphocytes enhance the functions monocytes and macrophages , regulate NK cells [2, 3], and support the action of B lymphocytes  and cytotoxic CD8 T cells. Recently, Swiss scientists have demonstrated that a small subset of CD4 T lymphocytes (Th-CTX cells) is capable of directly killing tumor cells .
In the 1980s, a team led by Prof. Drew Pardoll at John Hopkins University has shown that CD4 T lymphocytes can also become inactive while remaining alive , acquiring a status termed anergy, in which they proliferate less and produce less cytokines. CD4 T lymphocyte anergy is a physiological phenomenon that plays a role in establishing tolerance to markers of self and prevents auto-immune responses .
CD4 T lymphocyte anergy also occurs in pathological conditions, preventing necessary immune responses and therefore contributing to the establishment of chronic diseases associated with immune deficiencies. Sometimes accompanied by CD4 T lymphocyte depletion, anergy has been observed in several infectious contexts, including bacterial [8, 9, 10], viral [11, 12, 13, 14, 15] and parasitic infections . Anergic CD4 T lymphocytes have also been observed in a number of solid and blood cancers arguing that their unresponsive state may hinder the establishment of an efficient anti-tumor immune response [17: Colorectal Cancer, Metastatic cancers, Review T cell anergy, Pancreatic cancer ]. Reverting the anergic status of CD4 T lymphocytes has therefore emerged as an attractive therapeutic means to restore functional immunity in these pathological contexts.
Restoring CD4 T-cell function in HIV positive and cancer patients with DIACC1010
The immune deficiency that characterizes most HIV-infected patients is intimately linked to dysfunctional CD4 T lymphocytes. This immune deficiency is also observed in cancers. Fewer than 10% of circulating CD4 T lymphocytes are effectively infected by the virus  and yet the overall numbers of these cells progressively decline, resulting in CD4 lymphopenia (an abnormally low number of CD4 T lymphocytes in the blood), and the remaining cells display profound functional defects . Over the years, research by Prof. Jacques Thèze and colleagues has largely contributed to characterizing these CD4 T lymphocyte dysfunctions. In particular, they demonstrated that the CD4 T lymphocytes became unresponsive to stimulation by the IL-7 and IL-2 cytokines, due to the under-expression and dysfunction of their surface receptors, IL-2R and IL-7R [20, 21, 22], resulting in failure to activate the intracellular signaling pathway JAK/STAT [23, 24, 25].
In a study published by Pr. Thèze’s group in 2020, the scientists examined dysfunctional CD4 T lymphocytes by stimulated emission depletion microscopy and showed that over 80% of resting cells from viremic patients (VP) had a “bumpy” appearance owing to the presence of abnormally large membrane microdomains at their surface (aMMDs, >200nm). This unusual morphological feature was absent from CD4 T lymphocytes in healthy donors (HD) . Upon stimulation with IL-7, bumpy CD4 T lymphocytes from VP remained morphologically unchanged and unresponsive. They do not enable JAK/STAT signal transduction (resulting in nuclear translocation of phosphorylated STAT 5 protein), unlike CD4 T lymphocytes from healthy subjects, which become activated and whose membrane reorganizes in a physiological manner.
The researchers then demonstrated that plasma from HIV-positive patients could make CD4 T lymphocytes from healthy subjects insensitive to stimulation by IL-7 (reduction of pSTAT5 nuclear translocation), which suggests that a blood factor is responsible for this anergy.
Biochemical analysis of plasma from HIV-positive patients then identified the culprit: the PLA2G1B phospholipase. In vitro, this enzyme induces the digestion of the CD4 T lymphocyte membrane. This digestion is increased in the presence of the viral protein gp41 which acts as a cofactor, probably targeting the phospholipase on the surface of CD4 T lymphocytes.
Anti-PLA2G1B antibody DIACC1010 to restore CD4 T lymphocyte function in HIV and potentially in cancer
To counter the effects of PLA2G1B on CD4 T lymphocytes, the researchers developed a human monoclonal antibody (mAb) that inhibits the enzymatic activity of the protein. In vitro, the anti-PLA2G1B mAb restores CD4 T lymphocyte response to cytokine stimulation by IL-7 (as indicated by the nuclear translocation of phospho-STAT5). In vivo, the antibody prevents CD4 T lymphocyte anergy in mice. Given its ability to restore CD4 T lymphocyte response to IL-7, DIAC1010 seems to be a promising immunotherapeutic candidate to restore CD4 T lymphocyte functions anergy in HIV-positive patients.
The current treatment of HIV-infected patients consists of antiretroviral therapy (ART). In addition to controlling viremia, this triple combination therapy leads to full recovery of CD4 T lymphocyte numbers and function in 80% of patients, who display a near to normal life expectancy. However, up to 20% of HIV patients under ART present persistently low counts of CD4 T lymphocytes and are at higher risk of developing other diseases, including cancer. DIACC1010 is a promising treatment, complementary to ART, that could restore CD4 repertoire and function in these patients.
Figure 1: mechanism of action of DIACC1010
Healthy CD4 T lymphocytes form physiological membrane microdomains (pMMDs) upon activation with IL-7 and respond by activating JAK/STAT5 signaling. In HIV-positive patients, the PLA2G1B phospholipase acts in concert with a pathogenic peptide, the gp41 cofactor, to induce the formation of abnormal membrane microdomains (aMMDs) which trap surface proteins such as the IL-7 receptor (IL-7R) and block their function. The resulting “bumpy CD4 T lymphocytes” become anergic and fail to activate the JAK/STAT5 pathway in response to IL-7 stimulation. Through the blockade of PLA2G1B, DIACC1010 could restore functionality of CD4 T lymphocytes and thus enable them to fight the virus efficiently.
DIACC1010 in other pathological contexts and cancers
To identify the potential role of PLA2G1B in other pathologies associated with CD4 immunodeficiency, the Diaccurate team screened public databases for proteins that would contain sequences similar to the 3S sequence of the viral protein gp41. They found that ten human pathogens (beyond HIV) had such sequences, suggesting that the mechanism of CD4 T lymphocyte inactivation by the PLA2G1B-3S-peptide duo may be a universal mechanism. Among the 3S-type peptides identified is a peptide from Porphyromonas gingivalis, a bacterium responsible for gingivitis whose presence is also strongly associated with an increased risk of pancreatic cancer .
CD4 T lymphocytes seem to play an important role in the immune dysfunctions found in pancreatic cancer. Thus, in the presence of pancreatic cancer cells, CD4 T lymphocytes have reduced proliferation and migration abilities and their differentiation is modified . Diaccurate scientists have also shown that, as in HIV, plasma from pancreatic cancer patients renders CD4 T lymphocytes insensitive to stimulation by IL-7 and that this effect is abolished with the anti-PLA2G1B DIACC3010. Taken together, these results suggest that PLA2G1B, in conjunction with a Porphyromonas gingivalis-derived 3S-type cofactor, is responsible for triggering CD4 T lymphocyte anergy in pancreatic cancer. Hence the development program for the anti-PLA2G1B DIACC1010 in this indication.
Preclinical studies to characterize DIACC1010 immunopharmacological functions in HIV are currently under way. The company intends to establish a partnership with a leader in the field to confirm the potential of the anti-PLA2G1B immunotherapy mAb in SHIV models (the gold standard for preclinical development in HIV) then in HIV-infected patients.
In 2021, Diaccurate initiated a research program in oncology to validate cancer co-factors, assess PLA2G1B expression profile in different tumors and develop various tools such as surrogate anti-mouse PLA2G1B antibody and mouse models. The objective is to establish an actionable preclinical Proof-of-Concept of DIACC1010 in solid tumors in 2022 and initiate human clinical trials by 2024.
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