CD2-CD48 interactions promote cytotoxic T lymphocyte induction and function: anti-CD2 and anti-CD48 antibodies impair cytokine synthesis, proliferation, target recognition/adhesion, and cytotoxicity

Co-Stimulatory Receptors in Cancers and Their Implications for Cancer Immunotherapy

Immune checkpoint inhibitors (ICIs), including anti-PD-1 and anti-CTLA-4 therapeutic agents, are now approved by the Food and Drug Administration for treatment of various types of cancer. However, the therapeutic efficacy of ICIs varies among patients and cancer types. Moreover, most patients do not develop durable antitumor responses after ICI therapy due to an ephemeral reversal of T-cell dysfunction. As co-stimulatory receptors play key roles in regulating the effector functions of T cells, activating co-stimulatory pathways may improve checkpoint inhibition efficacy, and lead to durable antitumor responses. Here, we review recent advances in our understating of co-stimulatory receptors in cancers, providing the necessary groundwork for the rational design of cancer immunotherapy.

TGF-β regulated leukemia cell susceptibility against NK targeting through the down-regulation of the CD48 expression

Transforming growth factor-β (TGF-β) is known to function as a dual role regulatory cytokine for being either a suppresser or promoter during tumor initiation and progression. In solid tumors, TGF-β secreted from tumor microenvironment acts as a suppresser against host immunity, like natural killer (NK) cells, to favor tumor evasion. However, besides solid tumors, the underlying mechanism of how TGF-β regulates leukemogenesis, tumor progression, immunoediting, and NK function is still not clear in detail. In this study, we found that TGF-β induced leukemia MEG-01 and U937 cells to become less sensitive to NK-92MI targeting by down-regulating CD48, a ligand for NK activating receptor 2B4, but not down-regulating other tumor-associated carbohydrate antigens (TACAs). In CD48-knockdown cells, cells responding to NK-92MI targeting displayed a phenotype of less NK susceptibility and cell conjugation. On the other hand, when NK cells were treated with TGF-β, TGF-β suppressed NK recognition, degranulation, and killing activity in time-dependent manner by regulating ICAM-1 binding capacity instead of affecting expressions of activating and inhibitory receptors. Taken together, both leukemia cells and immune NK cells could be regulated by TGF-β through suppressing leukemia cell surface CD48 to escape from host surveillance and down-regulating NK cell surface ICAM-1 binding activity to impair NK functions, respectively. Our results suggested that TGF-β had effect in leukemia similar to that observed in solid tumors but through different regulatory mechanism.

A dynamic transcriptomic atlas of cytokine-induced killer cells

Several clinical immunotherapy trials with cytokine-induced killer (CIK) cells have been reported. However, molecular evidence of cell expansion, acquisition of tumor cytotoxicity, and safety of CIK cells is required before putting them to clinical use. Here, we performed dynamic transcriptomic analyses of CIKs generated from primary peripheral blood mononuclear cells exposed to interferon-γ, OKT3, and interleukin-2. CIK mRNAs were extracted and sequenced at days 0, 1, 7, and 14 and subjected to bioinformatics analyses. Using weighted correlation network analysis (WGCNA), we identified two major gene modules that mediate immune cell activation and mitosis. We found that activation and cytotoxicity of CIK cells likely rely on cluster of differentiation 8 (CD8) and its protein partner LCK proto-oncogene, Src family tyrosine kinase (LCK). A time-course series analysis revealed that CIK cells have relatively low immunogenicity because of decreased expression of some self-antigens. Importantly, we identified several crucial activating receptors and auxiliary adhesion receptors expressed on CIK cells that may function as tumor sensors. Interestingly, cytotoxicity-associated genes, including those encoding PRF1, GZMB, FASL, and several cytokines, were up-regulated in mature CIK cells. Most immune-checkpoint molecules and inflammatory tumor-promoting factors were down-regulated in the CIK cells, suggesting efficacy and safety in future clinical trials. Notably, insulin-like growth factor 1 (IGF-1) was highly expressed in CIK cells and may promote cytotoxicity, although it also could facilitate tumorigenesis. The transcriptomic atlas of CIK cells presented here may inform efforts to improve CIK-associated tumor cytotoxicity and safety in clinical trials.

Inhibition of cell adhesion and immune responses in the mouse model of collagen-induced arthritis with a peptidomimetic that blocks CD2-CD58 interface interactions

CD2 and CD58 are two important costimulatory molecules involved in generating the signal II required for normal immune signaling. However, this interaction can be targeted to be of benefit in cases of abnormal immune signaling seen in autoimmune diseases. Our objective in this study was to design a peptidomimetic (compound 7) based on a β-strand structure of the adhesion domain of CD2 protein to inhibit CD2-CD58 protein-protein interaction and its effect on immunomodulation in the collagen-induced arthritis (CIA) model. The ability of compound 7 to bind to CD58 protein was assessed using flow cytometry. The effect of compound 7 on modulating the immune response was evaluated in an autoimmune disease using CIA in mice. The stability of compound 7 was evaluated in mouse serum using mass spectrometry. Antibody (Ab) binding inhibition studies suggested that compound 7 binds to CD58 protein. Compound 7 was successful in modulating immune responses when administered in the CIA mouse model along with reducing anti-collagen Ab levels and decreasing the level of interferon gamma (IFN-γ) relative to control treatments. Compound 7 was found to be nonimmunogenic and stable in mouse serum up to 48 h. Results suggest that compound 7 can serve as a lead compound for immunomodulation, and could be a therapeutic agent for the autoimmune disease rheumatoid arthritis (RA).

Roles of CD48 in regulating immunity and tolerance

CD48, a member of the signaling lymphocyte activation molecule family, participates in adhesion and activation of immune cells. Although constitutively expressed on most hematopoietic cells, CD48 is upregulated on subsets of activated cells. CD48 can have activating roles on T cells, antigen presenting cells and granulocytes, by binding to CD2 or bacterial FimH, and through cell intrinsic effects. Interactions between CD48 and its high affinity ligand CD244 are more complex, with both stimulatory and inhibitory outcomes. CD244:CD48 interactions regulate target cell lysis by NK cells and CTLs, which are important for viral clearance and regulation of effector/memory T cell generation and survival. Here we review roles of CD48 in infection, tolerance, autoimmunity, and allergy, as well as the tools used to investigate this receptor. We discuss stimulatory and regulatory roles for CD48, its potential as a therapeutic target in human disease, and current challenges to investigation of this immunoregulatory receptor.

Exchange of cytosolic content between T cells and tumor cells activates CD4 T cells and impedes cancer growth

BACKGROUND

T cells are known to participate in the response to tumor cells and react with cytotoxicity and cytokine release. At the same time tumors established versatile mechanisms for silencing the immune responses. The interplay is far from being completely understood. In this study we show contacts between tumor cells and lymphocytes revealing novel characteristics in the interaction of T cells and cancer cells in a way not previously described.

METHODS/ FINDINGS

Experiments are based on the usage of a hydrophilic fluorescent dye that occurs free in the cytosol and thus transfer of fluorescent cytosol from one cell to the other can be observed using flow cytometry. Tumor cells from cell lines of different origin or primary hepatocellular carcinoma (HCC) cells were incubated with lymphocytes from human and mice. This exposure provoked a contact dependent uptake of tumor derived cytosol by lymphocytes--even in CD4⁺ T cells and murine B cells--which could not be detected after incubation of lymphocytes with healthy cells. The interaction was a direct one, not requiring the presence of accessory cells, but independent of cytotoxicity and TCR engagement. Electron microscopy disclosed 100-200 nm large gaps in the cell membranes of connected cells which separated viable and revealed astonishing outcome. While the lymphocytes were induced to proliferate in a long term fashion, the tumor cells underwent a temporary break in cell division. The in vitro results were confirmed in vivo using a murine acute lymphoblastic leukemia (ALL) model. The arrest of tumor proliferation resulted in a significant prolonged survival of challenged mice.

CONCLUSIONS

The reported cell-cell contacts reveal new characteristics i.e. the enabling of cytosol flow between the cells including biological active proteins that influence the cell cycle and biological behaviour of the recipient cells. This adds a completely new aspect in tumor induced immunology.

Structure-function studies of peptides for cell adhesion inhibition: identification of key residues by alanine mutation and peptide-truncation approach

Blockage of the interaction of CD2 with its ligand CD58 is expected to bring out potential therapeutic value for autoimmune diseases and organ transplantation. Three series of peptides (cVL, cIL and cAQ series) were designed from ratCD2 and humanCD2 to modulate CD2-CD58 interaction. To determine the specific segments in parent peptides responsible for inhibitory activity as lead sequence, we generated shorter fragments of the parent peptides and evaluated their biological activity with cell adhesion assay. The structure-activity relationship studies indicated that small cyclic peptides derived from CD2 ligand binding epitopes could mimic native beta-turn structure, and thus modulate CD2-CD58 interaction.

Gene expression in splenic CD4 and CD8 cells from BALB/c mice immunized with Porphyromonas gingivalis

BACKGROUND

T cells are fundamental in the pathogenesis of periodontal disease. Suppression of cell-mediated responses is associated with disease progression together with the concomitant increase in plaque pathogens including Porphyromonas gingivalis. The aim of the present study was to examine gene expression in T cells in response to P. gingivalis in mice.

METHODS

BALB/c mice were given weekly intraperitoneal injections of P. gingivalis outer-membrane antigens with Freund's incomplete adjuvant for 3 weeks, whereas control mice received phosphate buffered saline (PBS) and adjuvant only. Splenic CD4 and CD8 subpopulations were isolated by magnetic cell separation and their responses investigated using microarray analysis.

RESULTS

Most genes coded for enzymes concerned with metabolic pathways. Only five and 28 genes, respectively, were upregulated in CD4 and CD8 cells extracted from P. gingivalis-immunized mice, including immunoglobulin (Ig) heavy-chain genes for IgG1 and IgG2a in CD4 cells. In contrast, 1,141 and 1,175 genes, respectively, were downregulated. A total of 60 and 65 genes, respectively, coded for immune response proteins or those relevant to periodontal disease pathogenesis. The overlap of genes in the two subsets was 21%. One of the major effects, apart from T-cell function suppression, was the shift away from Th1 responses, although there was also a downregulation of two genes and upregulation of one Th2-response gene. Genes downregulated included those encoding cytokines, proteins involved in Ig binding, antigen presentation, innate immunity, extracellular matrix, and cell adhesion molecules that could result in dysregulation in the progressive periodontal lesion.

CONCLUSIONS

Early findings in humans demonstrated that periodontopathic bacteria induce immunosuppressive effects on T cells. The present study has shown that P. gingivalis had a predominant downregulatory effect on gene expression in CD4 and CD8 T cells in mice.

The CD2 family of natural killer cell receptors

The CD2 family of receptors is evolutionarily conserved and widely expressed on cells within the hematopoietic compartment. In recent years several new members have been identified with important roles in the immune system. CD2 family members regulate natural killer (NK) cell lytic activity and inflammatory cytokine production when engaged by ligands on tumor cells. Furthermore, a subfamily of CD2 receptors, the CD 150-like molecules, has been implicated in the pathogenesis of X-linked lymphoproliferative disease (XLP). Many of these receptors have now been shown to bind homophilically or heterophilically to other molecules within the family. With these discoveries a novel mechanism for lymphocyte regulation has emerged: CD2 family members on NK cells engage ligands on neighboring NK cells, leading to NK cell stimulation. Moreover, heterotypic stimulatory interactions between NK cells and other leukocytes also occur. In this manner, CD2 family members may provide interlymphocyte communication that maintains organization within the hematopoietic compartment and amplifies immune responses. This review discusses these multiple roles for CD2 family members, focusing specifically on the regulation of NK cells.

Optimization of methods to assess human mucosal T-cell responses to HIV infection

The majority of HIV-1 infections occur via sexual transmission at mucosal epithelia lining the vagina, cervix or rectum. Mucosal tissues also serve as viral reservoirs. However, our knowledge of human mucosal T-cell responses is limited. There is a need for reliable, sensitive, and reproducible methods for assessing mucosal immunity. Here we report on the collaborative efforts of two laboratories to optimize methods for processing, culturing, and analyzing mucosal lymphocytes. Rectal biopsy tissue was obtained by flexible sigmoidoscopy, which is rapid, minimally invasive, and well tolerated. Of the four methods compared for isolating mucosal mononuclear cells (MMC), collagenase digestion reproducibly yielded the most lymphocytes (4-7 x 10(6)). Furthermore, 0.5-1 x 10(6) MMC could be polyclonally expanded to yield 17 x 10(6) CD8+ T cells allowing mapping of responses to overlapping peptides spanning the HIV-1 genome using IFN-gamma enzyme-linked immunospot (ELISpot). Expansion also reduced the spontaneous IFN-gamma production normally detected in fresh MMC. Piperacillin-tazobactam and amphotericin B reduced contamination of MMC cultures to 4%. Taken together, these methods will be useful for studies of mucosal immunity to HIV-1 and other pathogens during natural infection and following vaccination.

Adenosine inhibits activation-induced T cell expression of CD2 and CD28 co-stimulatory molecules: role of interleukin-2 and cyclic AMP signaling pathways

Adenosine is an immunosuppressive molecule that is associated with the microenvironment of solid tumors. Mouse T cells activated with anti-CD3 antibody in the presence of adenosine with or without coformycin (to prevent adenosine breakdown by adenosine deaminase) exhibited decreased tyrosine phosphorylation of some intracellular proteins and were inhibited in their ability to proliferate and synthesize interleukin (IL)-2. In addition, adenosine interfered with activation-induced expression of the co-stimulatory molecules CD2 and CD28. Activation-induced CD2 and CD28 expression was also diminished when T cells were activated in the presence of anti-IL-2 and anti-CD25 antibodies to neutralize IL-2 bioactivity. Collectively, these data suggest that CD2 and CD28 up-regulation following T cell activation is IL-2-dependent; and that adenosine inhibits activation-induced T cell expression of CD2 and CD28 by interfering with IL-2-dependent signaling. The inhibitory effect of adenosine on activation-induced CD2 and CD28 expression could not be attributed to cyclic AMP (cAMP) accumulation resulting from the stimulation of adenylyl cyclase-coupled adenosine receptors, even though cAMP at concentrations much higher than those generated following adenosine stimulation was inhibitory for both CD2 and CD28 expression. We conclude that adenosine interferes with IL-2-dependent T cell expression of co-stimulatory molecules via a mechanism that does not involve the accumulation of intracellular cAMP.