Interaction of T-cell-specific adapter protein with Src- and Tec-family kinases

Adapter proteins are flexible and dynamic modulators of cellular signalling that are important for immune cell function. One of these, the T-cell-specific adapter protein (TSAd), interacts with the non-receptor tyrosine kinases Src and Lck of the Src family kinases (SFKs) and Itk of the Tec family kinases (TFKs). Three tyrosine residues in the TSAd C-terminus are phosphorylated by Lck and serve as docking sites for the Src homology 2 (SH2) domains of Src and Lck. The TSAd proline-rich region (PRR) binds to the Src homology 3 (SH3) domains found in Lck, Src and Itk. Despite known interactors, the role TSAd plays in cellular signalling remains largely unknown. TSAd's ability to bind both SFKs and TFKs may point to its function as a general scaffold for both kinase families. Using GST-pulldown as well as peptide array experiments, we found that both the SH2 and SH3 domains of the SFKs Fyn and Hck, as well as the TFKs Tec and Txk, interact with TSAd. This contrasts with Itk, which interacts with TSAd only through its SH3 domain. Although our analysis showed that TSAd is both co-expressed and may interact with Fyn, we were unable to co-precipitate Fyn with TSAd from Jurkat cells, as detected by Western blotting and affinity purification mass spectrometry. This may suggest that TSAd-Fyn interaction in intact cells may be limited by other factors, such as the subcellular localization of the two molecules or the co-expression of competing binding partners.

A novel SARS-CoV-2 Beta RBD DNA vaccine directly targeted to antigen-presenting cells induces strong humoral and T cell responses

Throughout the COVID-19 pandemic, several variants of concern (VoC) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have evolved, affecting the efficacy of the approved COVID-19 vaccines. To address the need for vaccines that induce strong and persistent cross-reactive neutralizing antibodies and T cell responses, we developed a prophylactic SARS-CoV-2 vaccine candidate based on our easily and rapidly adaptable plasmid DNA vaccine platform. The vaccine candidate, referred to here as VB2129, encodes a protein homodimer consisting of the receptor binding domain (RBD) from lineage B.1.351 (Beta) of SARS-CoV-2, a VoC with a severe immune profile, linked to a targeting unit (human LD78β/CCL3L1) that binds chemokine receptors on antigen-presenting cells (APCs) and a dimerization unit (derived from the hinge and CH3 exons of human IgG3). Immunogenicity studies in mice demonstrated that the APC-targeted vaccine induced strong antibody responses to both homologous Beta RBD and heterologous RBDs derived from Wuhan, Alpha, Gamma, Delta, and Omicron BA.1 variants, as well as cross-neutralizing antibodies against these VoC. Overall, preclinical data justify the exploration of VB2129 as a potential booster vaccine that induces broader antibody- and T cell-based protection against current and future SARS-CoV-2 VoC.

Abstract 3558: A novel and versatile cytokine empowered DNA vaccine platform with superior immune activating potential

Immunotherapy, in particular Immune Checkpoint Blockade (ICB) has been regarded as the next standard of care for many solid tumor indications. Yet, a significant proportion of patients do not respond to therapy. More specifically, failure of ICB has been linked to the absence of an anti-tumor immune response that can be boosted or revitalized. Cancer vaccines that are designed to elicit such response by educating the host immune system to recognize tumor antigens, are therefore considered a key next generation therapeutic modality for the treatment of human cancers.

Various vaccine platforms have been developed over the years, but recent advances in delivery technologies combined with the intrinsic qualities of the DNA matrix have positioned DNA vaccines as a safe and flexible alternative to other types of vaccine technologies. Vaccibody is developing DNA vaccines that allows specific targeting of tumors antigens to Antigen Presenting Cells (APCs), thus maximizing the elicited immune response.

Here we present a second-generation version of our DNA platform in which our vaccibody molecule can be co-expressed with immune-stimulatory proteins from one plasmid using a multicistronic design. Compared to the vaccibody molecule alone the simultaneous expression of selected immune stimulatory cytokines was shown to boost the overall immune response almost 3-fold to drive a potent anti-tumor response.

These data demonstrate the flexibility and potential of DNA vaccines as well as the advantages of combining an APC targeted delivery of tumor specific antigens together with a local production of immune stimulatory proteins.

Citation Format: Audun Beraas, Pierre Dillard, Judith Jing Wong, Christian Winther Wold, Eirik Solbakken, Linn Guro Oslen, Joel Benjamin Heim, Stalin Chellappa, Agnete Fredriksen, Mikkel Wandahl Pedersen, Stine Granum. A novel and versatile cytokine empowered DNA vaccine platform with superior immune activating potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3558.

The SH3 domains of the protein kinases ITK and LCK compete for adjacent sites on T cell-specific adapter protein

T-cell activation requires stimulation of specific intracellular signaling pathways in which protein-tyrosine kinases, phosphatases, and adapter proteins interact to transmit signals from the T-cell receptor to the nucleus. Interactions of LCK proto-oncogene, SRC family tyrosine kinase (LCK), and the IL-2-inducible T cell kinase (ITK) with the T cell-specific adapter protein (TSAD) promotes LCK-mediated phosphorylation and thereby ITK activation. Both ITK and LCK interact with TSAD's proline-rich region (PRR) through their Src homology 3 (SH3) domains. Whereas LCK may also interact with TSAD through its SH2 domain, ITK interacts with TSAD only through its SH3 domain. To begin to understand on a molecular level how the LCK SH3 and ITK SH3 domains interact with TSAD in human HEK293T cells, here we combined biochemical analyses with NMR spectroscopy. We found that the ITK and LCK SH3 domains potentially have adjacent and overlapping binding sites within the TSAD PRR amino acids (aa) 239-274. Pulldown experiments and NMR spectroscopy revealed that both domains may bind to TSAD aa 239-256 and aa 257-274. Co-immunoprecipitation experiments further revealed that both domains may also bind simultaneously to TSAD aa 242-268. Accordingly, NMR spectroscopy indicated that the SH3 domains may compete for these two adjacent binding sites. We propose that once the associations of ITK and LCK with TSAD promote the ITK and LCK interaction, the interactions among TSAD, ITK, and LCK are dynamically altered by ITK phosphorylation status.

Abstract 5003: Vaccibody DNA vaccine platform VB10.NEO induces strong neo-antigen specific CD8+ T cell responses critical to cure established tumors in pre-clinical models

BACKGROUND: Recent advances in the field of cancer immunotherapy have identified CD8+ T cell responses against tumor-specific neoantigens as a key driver of tumor regression and prolonged survival. VB10.NEO is a highly potent DNA plasmid vaccine with intrinsic adjuvant effect designed for efficient delivery of personalized tumor-specific neoantigens. VB10.NEO plasmid is translated in vivo and the secreted protein will covalently bind to endocytic receptors on APC by a targeting unit expressing CCL3 (MIP-1α) allowing efficient uptake and presentation of the neoantigens. In addition, CCL3 will attract immune cells by chemotaxis and induce maturation of APC locally. The objective of this study is to demonstrate the potential of VB10.NEO to induce tumor-specific T cell responses and control tumor growth.

METHODS: VB10.NEO was delivered i.m to study CD8+ and CD4+ neoantigen-specific T cell responses in four different pre-clinical mouse models. Immunogenicity was compared with delivery of neoantigen as traditional peptide-adjuvant immunization. The tumor protective effect of VB10.NEO in the presence or absence of anti-PD-1 therapy was investigated in the CT26 colon carcinoma model.

RESULTS: Vaccibody DNA Vaccine Platform VB10.NEO is flexible and can hold up to at least 40 neoepitopes. VB10.NEO vaccination induced strong neoantigen-specific T cell responses. Homologous boost vaccinations further augmented the response. T cell responses against predicted CD8+ T cell epitopes previously reported as non-immunogenic or activating only weak T cell responses using a conventional peptide-adjuvant or RNA immunization showed strong CD8+ T cell responses when delivered in the Vaccibody format, demonstrating a unique and strong priming of CD8+ T cells using VB10.NEO. The response was also accompanied by CD4+ T cell responses. In a therapeutic tumor setting VB10.NEO vaccinated mice (monotherapy) induced tumor protective responses. The effect was augmented when combining VB10.NEO with anti-PD-1 where complete regression of large established tumors was observed. All tumour-free mice rechallenged with a lethal tumor dose were protected indicating induction of long-lasting memory responses. Furthermore, the critical role of CD8+ T cells for the observed tumour protection was confirmed when depleting CD8+ T cells.

CONCLUSION: VB10.NEO immunotherapy induce strong CD8+ T cell responses critical for anti-tumor effect which demonstrate the unique characteristic of the Vaccibody platform to potentiate activation of CD8+ T cells. VB10.NEO in combination with anti-PD-1 further synergize the potent immune responses resulting in durable complete tumor regression in pre-clinical models supporting the scientific rational for the current ongoing clinical trial investigating VB10.NEO in combination with CPI in patients with advanced solid tumors.

Citation Format: Elisabeth Stubsrud, Stine Granum, Helene Zell-Flagstad, Audun Bersaas, Lise Madelene Skullerud, Monika Sekelja, Karoline Schjetne, Agnete Fredriksen. Vaccibody DNA vaccine platform VB10.NEO induces strong neo-antigen specific CD8+ T cell responses critical to cure established tumors in pre-clinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5003.

Abstract 2256: Combination of neoantigen DNA plasmid vaccine VB10.NEO and NKTR-214, a CD122-biased immunostimulatory cytokine, induces strong neoantigen-specific T cell responses and sustained tumor regression in pre-clinical models

BACKGROUND: VB10.NEO is a highly potent DNA plasmid vaccine with intrinsic adjuvant effect designed for efficient delivery of personalized neoepitopes and is currently being tested in combination with CPI in patients with advanced solid tumors. NKTR-214, a CD122-biased agonist that targets the IL-2 pathway, provides sustained signaling through the heterodimeric IL-2 receptor pathway (IL-2Rβγ) to preferentially activate and expand NK and effector CD8+ T cells over T-regulatory cells, and is currently in multiple phase I, II and III clinical trials in combination with nivolumab. Here we explored the combination of VB10.NEO with NKTR-214 in the presence or absence of anti-PD-1 therapy in different pre-clinical syngeneic tumor models.

METHODS: Mice were vaccinated with VB10.NEO (i.m.), NKTR-214 (i.v) and anti-PD-1 (i.p.) at different intervals to study efficacy and optimal dosing schedule before spleens were harvested to analyze CD8+ and CD4+ neoantigen-specific T cell responses in IFN-γ ELISpot in two different tumor models (B16 and CT26). The tumor protective effect of the combination therapy of VB10.NEO with NKTR-214 in the presence or absence of anti-PD-1 therapy was investigated in CT26 colon carcinoma model.

RESULTS: Combination of VB10.NEO and NKTR-214 greatly synergizes, resulting in 5-fold increase in the number of neoantigen-specific T cell responses compared to VB10.NEO alone. Dosing of VB10.NEO vaccination relative to NKTR-214 administration was found to impact the extent of the synergetic activity. Mice treated with VB10.NEO containing 10 neoepitopes from B16 in combination with NKTR-214 showed both a stronger response to each neoantigen, but also to increased numbers of neoantigens, showing that both the breadth and depth of the immune response were elevated. The VB10.NEO and NKTR-214 combination showed an even more evident effect on CD8+ T cell responses as the combination elicited a neoantigen-specific CD8+ T cell response against 10 neoantigens compared to 5 neoantigens with VB10.NEO alone, further strengthening the combination’s ability to induce strong neoantigen-specific CD8+ T cell responses. In the therapeutic tumor model, increased number of complete responders was observed in mice treated with the triple combination of vaccine, NKTR-214 and CPI demonstrating the strong rational for bringing together these unique and non-overlapping mechanisms that create an effective treatment of established tumors.

CONCLUSION: VB10.NEO in combination with NKTR-214 with or without anti-PD-1 therapy synergizes to elicit greater breadth and depth of neoantigen-specific T cell responses and provide durable complete tumor regression in pre-clinical models supporting the rationale for examining the combination clinically.

Citation Format: Stine Granum, Helene Zell-Flagstad, Audun Bersaas, Lise Skullerud, Elisabeth Müller, Mads Axelsen, Karoline Schjetne, Jonathan Zalevsky, Agnete Fredriksen. Combination of neoantigen DNA plasmid vaccine VB10.NEO and NKTR-214, a CD122-biased immunostimulatory cytokine, induces strong neoantigen-specific T cell responses and sustained tumor regression in pre-clinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2256.

T cell specific adaptor protein (TSAd) promotes interaction of Nck with Lck and SLP-76 in T cells

Background

The Lck and Src binding adaptor protein TSAd (T cell specific adaptor) regulates actin polymerization in T cells and endothelial cells. The molecular details as to how TSAd regulates this process remain to be elucidated.

Results

To identify novel interaction partners for TSAd, we used a scoring matrix-assisted ligand algorithm (SMALI), and found that the Src homology 2 (SH2) domain of the actin regulator Non-catalytic region of tyrosine kinase adaptor protein (Nck) potentially binds to TSAd phosphorylated on Tyr²⁸⁰ (pTyr²⁸⁰) and pTyr³⁰⁵. These predictions were confirmed by peptide array analysis, showing direct binding of recombinant Nck SH2 to both pTyr²⁸⁰ and pTyr³⁰⁵ on TSAd. In addition, the SH3 domains of Nck interacted with the proline rich region (PRR) of TSAd. Pull-down and immunoprecipitation experiments further confirmed the Nck-TSAd interactions through Nck SH2 and SH3 domains. In line with this Nck and TSAd co-localized in Jurkat cells as assessed by confocal microscopy and imaging flow cytometry. Co-immunoprecipitation experiments in Jurkat TAg cells lacking TSAd revealed that TSAd promotes interaction of Nck with Lck and SLP-76, but not Vav1. TSAd expressing Jurkat cells contained more polymerized actin, an effect dependent on TSAd exon 7, which includes interactions sites for both Nck and Lck.

Conclusions

TSAd binds to and co-localizes with Nck. Expression of TSAd increases both Nck-Lck and Nck-SLP-76 interaction in T cells. Recruitment of Lck and SLP-76 to Nck by TSAd could be one mechanism by which TSAd promotes actin polymerization in activated T cells.

SH2D2A modulates T cell mediated protection to a B cell derived tumor in transgenic mice

Background

T cell specific adapter protein (TSAd), encoded by the SH2D2A gene, modulates signaling downstream of the T cell receptor (TCR). Young, unchallenged SH2D2A-deficient C57BL/6 mice exhibit a relatively normal immune phenotype. To address whether SH2D2A regulates physiologic immune responses, SH2D2A-deficient TCR-transgenic BALB/c mice were generated. The transgenic TCR recognizes a myeloma-derived idiotypic (Id) peptide in the context of the major histocompatibility complex (MHC) class II molecule I-E^d, and confers T cell mediated resistance to transplanted multiple myeloma development in vivo.

Principal Findings

The immune phenotype of SH2D2A-deficient C57BL/6 and BALB/c mice did not reveal major differences compared to the corresponding wild type mice. When challenged with myeloma cells, Id-specific TCR-transgenic BALB/c mice lacking SH2D2A displayed increased resistance towards tumor development. Tumor free TCR-transgenic SH2D2A-deficient mice had higher numbers of Id-specific single positive CD4+ thymocytes compared to TCR-transgenic wild-type mice.

Conclusion

Our results suggest a modulatory role for SH2D2A in T cell mediated immune surveillance of cancer. However, it remains to be established whether its effect is T-cell intrinsic. Further studies are required to determine whether targeting SH2D2A function in T cells may be a potential adjuvant in cancer immunotherapy.

T cell specific adapter protein (TSAd) interacts with Tec kinase ITK to promote CXCL12 induced migration of human and murine T cells

Background

The chemokine CXCL12/SDF-1α interacts with its G-protein coupled receptor CXCR4 to induce migration of lymphoid and endothelial cells. T cell specific adapter protein (TSAd) has been found to promote migration of Jurkat T cells through interaction with the G protein β subunit. However, the molecular mechanisms for how TSAd influences cellular migration have not been characterized in detail.

Principal Findings

We show that TSAd is required for tyrosine phosphorylation of the Lck substrate IL2-inducible T cell kinase (Itk). Presence of Itk Y511 was necessary to boost TSAd's effect on CXCL12 induced migration of Jurkat T cells. In addition, TSAd's ability to promote CXCL12-induced actin polymerization and migration of Jurkat T lymphocytes was dependent on the Itk-interaction site in the proline-rich region of TSAd. Furthermore, TSAd-deficient murine thymocytes failed to respond to CXCL12 with increased Itk phosphorylation, and displayed reduced actin polymerization and cell migration responses.

Conclusion

We propose that TSAd, through its interaction with both Itk and Lck, primes Itk for Lck mediated phosphorylation and thereby regulates CXCL12 induced T cell migration and actin cytoskeleton rearrangements.

Modulation of Lck function through multisite docking to T cell-specific adapter protein

T cell-specific adapter protein (TSAd), encoded by the SH2D2A gene, interacts with Lck through its C terminus and thus modulates Lck activity. Here we mapped Lck phosphorylation and interaction sites on TSAd and evaluated their functional importance. The three C-terminal TSAd tyrosines Tyr(280), Tyr(290), and Tyr(305) were phosphorylated by Lck and functioned as docking sites for the Lck Src homology 2 (SH2) domain. Binding affinities of the TSAd Tyr(P)(280) and Tyr(P)(290) phosphopeptides to the isolated Lck SH2 domain were similar to that observed for the Lck Tyr(P)(505) phosphopeptide, whereas the TSAd Tyr(P)(305) peptide displayed a 10-fold higher affinity. The proline-rich Lck SH3-binding site on TSAd as well as the Lck SH2 domain were required for efficient tyrosine phosphorylation of TSAd by Lck. Interaction sites on TSAd for both Lck SH2 and Lck SH3 were necessary for TSAd-mediated modulation of proximal TCR signaling events. We found that 20-30% of TSAd molecules are phosphorylated in activated T cells and that the proportion of TSAd to Lck molecules in such cells is approximately 1:1. Therefore, in activated T cells, a considerable number of Lck molecules may potentially be engaged by TSAd. In conclusion, Lck binds to TSAd prolines and phosphorylates and interacts with the three C-terminal TSAd tyrosines. We propose that through multivalent interactions with Lck, TSAd diverts Lck from phosphorylating other substrates, thus modulating its functional activity through substrate competition.

Expression of SH2D2A in T-cells is regulated both at the transcriptional and translational level

The T-cell specific adapter protein (TSAd) encoded by the SH2D2A gene is up-regulated in activated human CD4+ T-cells in a cAMP-dependent manner. Expression of SH2D2A is important for proper activation of T-cells. Here, we show that SH2D2A expression is regulated both at the transcriptional and translational level. cAMP signaling alone induces TSAd-mRNA expression but fails to induce increased TSAd protein levels. By contrast, TCR engagement provides signals for both TSAd transcription and translation. We further show that cAMP signaling can prime T-cells for a more prompt expression of TSAd protein upon TCR stimulation. Our study thus points to a novel mechanism for how cAMP signaling may modulate T-cell activation through transcriptional priming of resting cells.

Structure function analysis of SH2D2A isoforms expressed in T cells reveals a crucial role for the proline rich region encoded by SH2D2A exon 7

BACKGROUND

The activation induced T cell specific adapter protein (TSAd), encoded by SH2D2A, interacts with and modulates Lck activity. Several transcript variants of TSAd mRNA exist, but their biological significance remains unknown. Here we examined expression of SH2D2A transcripts in activated CD4+ T cells and used the SH2D2A variants as tools to identify functionally important regions of TSAd.

RESULTS

TSAd was found to interact with Lck in human CD4+ T cells ex vivo. Three interaction modes of TSAd with Lck were identified. TSAd aa239-256 conferred binding to the Lck-SH3 domain, whereas one or more of the four tyrosines within aa239-334 encoded by SH2D2A exon 7 was found to confer interaction with the Lck-SH2-domain. Finally the TSAd-SH2 domain was found to interact with Lck. The SH2D2A exon 7 encoding TSAd aa 239-334 was found to harbour information essential not only for TSAd interaction with Lck, but also for TSAd modulation of Lck activity and translocation of TSAd to the nucleus. All five SH2D2A transcripts were found to be expressed in CD3 stimulated CD4+ T cells.

CONCLUSION

These data show that TSAd and Lck may interact through several different domains and that Lck TSAd interaction occurs in CD4+ T cells ex vivo. Alternative splicing of exon 7 encoding aa239-334 results in loss of the majority of protein interaction motives of TSAd and yields truncated TSAd molecules with altered ability to modulate Lck activity. Whether TSAd is regulated through differential alternative splicing of the SH2D2A transcript remains to be determined.

The C?terminus of T?cell-specific adapter protein (TSAd) is necessary for TSAd-mediated inhibition of Lck activity

T cell-specific adapter protein (TSAd), encoded by the SH2D2A gene, is expressed in activated T cells. The function of TSAd is as yet unknown. We previously showed that TSAd may modulate T cell receptor-triggered signaling events. TSAd contains a Src homology (SH)2 domain, ten tyrosines and a C-terminal proline-rich region. Here, we show that human TSAd interacts with Lck through the Lck SH2 and SH3 domains and is a substrate for Lck. The TSAd C terminus, including the proline-rich region and five tyrosines, is both necessary and sufficient for TSAd interaction with and phosphorylation by Lck. Expression of TSAd in Jurkat TAg cells results in hyperphosphorylation of endogenous Lck on Y394 and to an even larger extent on Y505, resulting in a reduced Y394/Y505 phosphorylation ratio in these cells. Furthermore, full-length TSAd, but not TSAd lacking the C terminus, inhibits the hyperactive Lck Y505F mutant when both are expressed in Jurkat T cells. In contrast, expression of the TSAd C terminus alone is sufficient to inhibit Lck Y505F in phosphorylating its substrates in Jurkat T cells. Our results indicate that the TSAd C terminus is essential for inhibition of Lck activity by TSAd, and suggest a mechanism for how TSAd may inhibit early T cell activation events.