Cross-reactive and mono-reactive SARS-CoV-2 CD4+ T cells in prepandemic and COVID-19 convalescent individuals

Class II tetramer reagents for eleven common DR alleles and a DP allele prevalent in the world population were used to identify SARS-CoV-2 CD4+ T cell epitopes. A total of 112, 28 and 42 epitopes specific for Spike, Membrane and Nucleocapsid, respectively, with defined HLA-restriction were identified. Direct ex vivo staining of PBMC with tetramer reagents was used to define immunodominant and subdominant T cell epitopes and estimate the frequencies of these T cells in SARS-CoV-2 exposed and naïve individuals. Majority of SARS-CoV-2 epitopes identified have <67% amino acid sequence identity with endemic coronaviruses and are unlikely to elicit high avidity cross-reactive T cell responses. Four SARS-CoV-2 Spike reactive epitopes, including a DPB1*04:01 restricted epitope, with ≥67% amino acid sequence identity to endemic coronavirus were identified. SARS-CoV-2 T cell lines for three of these epitopes elicited cross-reactive T cell responses to endemic cold viruses. An endemic coronavirus Spike T cell line showed cross-reactivity to the fourth SARS-CoV-2 epitope. Three of the Spike cross-reactive epitopes were subdominant epitopes, while the DPB1*04:01 restricted epitope was a dominant epitope. Frequency analyses showed Spike cross-reactive T cells as detected by tetramers were present at relatively low frequency in unexposed people and only contributed a small proportion of the overall Spike-specific CD4+ T cells in COVID-19 convalescent individuals. In total, these results suggested a very limited number of SARS-CoV-2 T cells as detected by tetramers are capable of recognizing ccCoV with relative high avidity and vice versa. The potentially supportive role of these high avidity cross-reactive T cells in protective immunity against SARS-CoV-2 needs further studies.

PODO447: a novel antibody to a tumor-restricted epitope on the cancer antigen podocalyxin

BackgroundThe success of new targeted cancer therapies has been dependent on the identification of tumor-specific antigens. Podocalyxin (Podxl) is upregulated on tumors with high metastatic index and its presence is associated with poor outcome, thus emerging as an important prognostic and theragnostic marker in several human cancers. Moreover, in human tumor xenograft models, Podxl expression promotes tumor growth and metastasis. Although a promising target for immunotherapy, the expression of Podxl on normal vascular endothelia and kidney podocytes could hamper efforts to therapeutically target this molecule. Since pathways regulating post-translational modifications are frequently perturbed in cancer cells, we sought to produce novel anti-Podxl antibodies (Abs) that selectively recognize tumor-restricted glycoepitopes on the extracellular mucin domain of Podxl.MethodsSplenic B cells were isolated from rabbits immunized with a Podxl-expressing human tumor cell line. Abs from these B cells were screened for potent reactivity to Podxl+ neoplastic cell lines but not Podxl+ primary endothelial cells. Transcripts encoding heavy and light chain variable regions from promising B cells were cloned and expressed as recombinant proteins. Tumor specificity was assessed using primary normal tissue and an ovarian cancer tissue microarray (TMA). Mapping of the tumor-restricted epitope was performed using enzyme-treated human tumor cell lines and a glycan array.ResultsOne mAb (PODO447) showed strong reactivity with a variety of Podxl+ tumor cell lines but not with normal primary human tissue including Podxl+ kidney podocytes and most vascular endothelia. Screening of an ovarian carcinoma TMA (219 cases) revealed PODO447 reactivity with the majority of tumors, including 65% of the high-grade serous histotype. Subsequent biochemical analyses determined that PODO447 reacts with a highly unusual terminal N-acetylgalactosamine beta-1 (GalNAcβ1) motif predominantly found on the Podxl protein core. Finally, Ab–drug conjugates showed specific efficacy in killing tumor cells in vitro.ConclusionsWe have generated a novel and exquisitely tumor-restricted mAb, PODO447, that recognizes a glycoepitope on Podxl expressed at high levels by a variety of tumors including the majority of life-threatening high-grade serous ovarian tumors. Thus, tumor-restricted PODO447 exhibits the appropriate specificity for further development as a targeted immunotherapy.

Three adjacent nucleotide changes spanning two residues in SARS-CoV-2 nucleoprotein: possible homologous recombination from the transcription-regulating sequence

The COVID-19 pandemic is caused by the single-stranded RNA virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus of zoonotic origin that was first detected in Wuhan, China in December 2019. There is evidence that homologous recombination contributed to this cross-species transmission. Since that time the virus has demonstrated a high propensity for human-to-human transmission. Here we report two newly identified adjacent amino acid polymorphisms in the nucleocapsid at positions 203 and 204 (R203K/G204R) due to three adjacent nucleotide changes across the two codons (i.e. AGG GGA to AAA CGA). This new strain within the LGG clade may have arisen by a form of homologous recombination from the core sequence (CS-B) of the transcription-regulating sequences of SAS-CoV-2 itself and has rapidly increased to approximately one third of reported sequences from Europe during the month of March 2020. We note that these polymorphisms are predicted to reduce the binding of an overlying putative HLA-C*07-restricted epitope and that HLA-C*07 is prevalent in Caucasians being carried by >40% of the population. The findings suggest that homologous recombination may have occurred since its introduction into humans and be a mechanism for increased viral fitness and adaptation of SARS-CoV-2 to human populations.

Identification of HLA-A0201 restricted epitope of novel cancer/testis antigens VCX/Y and generation of antigen-specific T-cell receptor engineered T cells for treatment of solid tumor malignancies.

160 Background: To identify HLA-A0201 restricted epitope of novel cancer/testis antigen VCX/Y, generate antigen specific T cells and T-cell receptor (TCR) engineered T cells for adoptive cell therapy (ACT) of solid cancer patients. Methods: Reverse-immunology method was used to identify HLA-A0201 restricted epitope of VCX/Y. The high binding score peptide or whole length of VCX3A mRNA were pulsed or transfected to mature dendritic cells (mDC) from HLA-A0201+ donor and then stimulated autologous naïve T cells. Tetramer guided sorting were performed to purify the epitope specific T cells and CTL clones were generated with limiting dilution. TCR were cloned out from high activity CTL clone and the recombinant of retrovirus vector were constructed to introduce the TCR to allogeneic PBMC to generate the TCR engineered T cells. Results: One peptide which its sequence was shared with all VCX/Y members was identified. Interesting, only CTL clone generated from simulation of VCX3A mRNA transfected DC can recognize naturally processed VCX/Y presented by HLA-A0201+ tumor cells. Cold target inhibition detection confirmed that this VCX/Y peptide was naturally processed and recognized by HLA-A0201+ CTL clone. After infection of retrovirus containing the TCR from high activity of CTL clone, the TCR engineered T cells can recognize HLA-A2+ tumor cells but not normal lung cells. Moreover, these TCR engineered T cells specifically secreted IFN-γ in response to T2 cells pulsed with peptide, as well as HLA-A0201+ and VCX/Y overexpressed tumor cells. Conclusions: VCX/Y peptide we identified is a novel candidate peptide antigen for vaccine or for endogenous adoptive T cell therapy. The correlated high activity TCR gene can generate TCR engineered T cells from patients with anti-tumor activity and offer an alternative adoptive T cell treatment for patients with VCX/Y expressing solid tumor malignancies.

PARV4 prevalence, phylogeny, immunology and coinfection with HIV, HBV and HCV in a multicentre African cohort

Background: The seroprevalence of human parvovirus-4 (PARV4) varies considerably by region. In sub-Saharan Africa, seroprevalence is high in the general population, but little is known about the transmission routes or the prevalence of coinfection with blood-borne viruses, HBV, HCV and HIV. Methods: To further explore the characteristics of PARV4 in this setting, with a particular focus on the prevalence and significance of coinfection, we screened a cohort of 695 individuals recruited from Durban and Kimberley (South Africa) and Gaborone (Botswana) for PARV4 IgG and DNA, as well as documenting HIV, HBV and HCV status. Results: Within these cohorts, 69% of subjects were HIV-positive. We identified no cases of HCV by PCR, but 7.4% were positive for HBsAg. PARV4 IgG was positive in 42%; seroprevalence was higher in adults (69%) compared to children (21%) (p<0.0001) and in HIV-positive (52%) compared to HIV-negative individuals (24%) (p<0.0001), but there was no association with HBsAg status. We developed an on-line tool to allow visualization of coinfection data (https://purl.oclc.org/coinfection-viz). We identified five subjects who were PCR-positive for PARV4 genotype-3. Ex vivo CD8+ T cell responses spanned the entire PARV4 proteome and we propose a novel HLA-B*57:03-restricted epitope within the NS protein. Conclusions: This characterisation of PARV4 infection provides enhanced insights into the epidemiology of infection and co-infection in African cohorts, and provides the foundations for planning further focused studies to elucidate transmission pathways, immune responses, and the clinical significance of this organism.