Mice devoid of T, B, and NK cells distinguish between self and allogeneic non-self despite the absence of an adaptive immune system. When challenged with an allograft they mount an innate response characterized by accumulation of mature, monocyte-derived dendritic cells (DCs) that produce IL-12 and initiate graft rejection. The molecular mechanisms, however, by which the innate immune system detects allogeneic non-self to generate these DCs are not known. To address this question, we studied the innate response of Rag2−/−γc−/− mice, which lack T, B, NK cells, to grafts from allogeneic donors. We identified by positional cloning that donor polymorphism in the gene encoding signal regulatory protein alpha (SIRPα) is a key modulator of the recipient’s innate allorecognition response. Donors that differed from the recipient in one or both Sirpa alleles elicited an innate alloresponse. The response was mediated by binding of donor SIRPα to recipient CD47 and was modulated by the strength of the SIRPα-CD47 interaction. Therefore, sensing SIRPα polymorphism by CD47 provides a molecular mechanism by which the innate immune system distinguishes between self and allogeneic non-self independently of T, B, and NK cells.

Immunological memory specific to previously encountered antigens is a cardinal feature of adaptive lymphoid cells. However, it is unknown whether innate myeloid cells retain memory of prior antigenic stimulation and respond to it more vigorously on subsequent encounters. In this work, we show that murine monocytes and macrophages acquire memory specific to major histocompatibility complex I (MHC-I) antigens, and we identify A-type paired immunoglobulin-like receptors (PIR-As) as the MHC-I receptors necessary for the memory response. We demonstrate that deleting PIR-A in the recipient or blocking PIR-A binding to donor MHC-I molecules blocks memory and attenuates kidney and heart allograft rejection. Thus, innate myeloid cells acquire alloantigen-specific memory that can be targeted to improve transplant outcomes.

Apoptosis is a natural process during animal development for the programmed removal of superfluous cells. During apoptosis general protein synthesis is reduced, but the synthesis of cell death proteins is enhanced. Selective translation has been attributed to modification of the protein synthesis machinery to disrupt cap-dependent mRNA translation and induce a cap-independent mechanism. We have previously shown that disruption of the balance between cap-dependent and cap-independent C. elegans eIF4G isoforms (IFG-1 p170 and p130) by RNA interference promotes apoptosis in developing oocytes. Germ cell apoptosis was accompanied by the appearance of the Apaf-1 homolog, CED-4. Here we show that IFG-1 p170 is a native substrate of the worm executioner caspase, CED-3, just as mammalian eIF4GI is cleaved by caspase-3. Loss of Bcl-2 function (ced-9ts) in worms induced p170 cleavage in vivo, coincident with extensive germ cell apoptosis. Truncation of IFG-1 occurred at a single site that separates the cap-binding and ribosome-associated domains. Site-directed mutagenesis indicated that CED-3 processes IFG-1 at a non-canonical motif, TTTD456. Coincidentally, the recognition site was located 65 amino acids downstream of the newly mapped IFG-1 p130 start site suggesting that both forms support cap-independent initiation. Genetic evidence confirmed that apoptosis induced by loss of ifg-1 p170 mRNA was caspase (ced-3) and apoptosome (ced-4/Apaf-1) dependent. These findings support a new paradigm in which modal changes in protein synthesis act as a physiological signal to initiate cell death, rather than occur merely as downstream consequences of the apoptotic event.

Ultimately, the production of new proteins in undetermined cells pushes them to new fates. Other proteins hold a stem cell in a mode of self-renewal. In germ cells, these decision-making proteins are produced largely from translational control of preexisting mRNAs. To date, all of the regulation has been attributed to RNA binding proteins (RBPs) that repress mRNAs in many models of germ cell development (Drosophila, mouse, C. elegans, and Xenopus). In this review, we focus on the selective, positive function of translation initiation factors eIF4E and eIF4G, which recruit mRNAs to ribosomes upon derepression. Evidence now shows that the two events are not separate but rather are coordinated through composite complexes of repressors and germ cell isoforms of eIF4 factors. Strikingly, the initiation factor isoforms are themselves mRNA selective. The mRNP complexes of translation factors and RBPs are built on specific populations of mRNAs to prime them for subsequent translation initiation. Simple rearrangement of the partners causes a dormant mRNP to become synthetically active in germ cells when and where they are required to support gametogenesis.

Regulated mRNA translation is vital for germ cells to produce new proteins in the spatial and temporal patterns that drive gamete development. Translational control involves the de-repression of stored mRNAs and their recruitment by eukaryotic initiation factors (eIFs) to ribosomes. C. elegans expresses five eIF4Es (IFE-1-IFE-5); several have been shown to selectively recruit unique pools of mRNA. Individual IFE knockouts yield unique phenotypes due to inefficient translation of certain mRNAs. Here, we identified mRNAs preferentially translated through the germline-specific eIF4E isoform IFE-1. Differential polysome microarray analysis identified 77 mRNAs recruited by IFE-1. Among the IFE-1-dependent mRNAs are several required for late germ cell differentiation and maturation. Polysome association of gld-1, vab-1, vpr-1, rab-7 and rnp-3 mRNAs relies on IFE-1. Live animal imaging showed IFE-1-dependent selectivity in spatial and temporal translation of germline mRNAs. Altered MAPK activation in oocytes suggests dual roles for IFE-1, both promoting and suppressing oocyte maturation at different stages. This single eIF4E isoform exerts positive, selective translational control during germ cell differentiation.

During apoptosis, activated caspases cleave the translation initiation factor eIF4G. This cleavage disrupts cap-dependent mRNA translation initiation within the cell. However, a specific subset of mRNAs can still be recruited for protein synthesis in a cap-independent manner by the residual initiation machinery. Many of these mRNAs, including cell death related mRNAs, contain internal ribosome entry sites (IRESes) that promote their enhanced translation during apoptosis. Still other mRNAs have little dependence on the cap recognition mechanism. The expression of the encoded proteins, both anti- and pro-apoptotic, allows for an initial period of attempted cell survival, then commitment to cell death when damage is extensive. In this study we address the translational regulation of the stress and apoptosis-related mRNAs in C. elegans: BiP (hsp-3) (hsp-4), Hif-1 (hif-1), p53 (cep-1), Bcl-2 (ced-9) and Apaf-1 (ced-4). Altered translational efficiency of these messages was observed upon depletion of cap-dependent translation and induction of apoptosis within the C. elegans gonad. Our findings suggest a physiological link between the cap-independent mechanism and the enhanced translation of hsp-3 and ced-9. This increase in the efficiency of translation may be integral to the stress response during the induction of physiological apoptosis.

e21213 Background: Lung cancer is the leading cause of death in males and females in the United States. Approximately 85% of all cases are classified as non-small cell lung cancer (NSCLC) with majority diagnosed at an advanced stage. Unfortunately, response to traditional chemotherapy (ChT) has been poor with a five-year survival rate of 6% in metastatic NSCLC. Immune checkpoint inhibitors (ICI) have changed the therapeutic landscape for advanced NSCLC and are being utilized alone or in combination with ChT as the standard first-line therapy. With widespread use of ICIs, immune-related adverse events (irAE) are commonly seen and in some studies their occurrence correlates with improved outcomes. The aim of our study was to evaluate whether development of irAEs has an impact on survival in NSCLC. Methods: We performed a retrospective analysis on stage IV NSCLC patients treated with ChT, ChT plus ICI, or ICI monotherapy from December 2016 to December 2019. Univariable and multivariable analyses identified characteristics predictive of progression-free survival (PFS) and overall survival (OS). OS was calculated using Kaplan Meier curves. Log-rank statistics were used to assess statistical significance between groups. Multivariable logistic regression was performed to identify predictors of survival. Results: 193 patients were evaluated out of which 92 (47.2%) received ChT plus pembrolizumab, 69 (35.4%) received pembrolizumab alone and 32 (16.4%) received ChT alone. 130 patients were found to have no irAEs compared to 57 patients who were noted to have any grade of irAE. The median PFS was 17.4 months (irAE group) vs. 8.5 months (non-irAE group) with hazard ratio (HR) of 0.58 (95% CI: 0.41 to 0.80, p = 0.001). The median OS was 29.4 months (irAE group) vs. 14.4 months (non-irAE group) with HR of 0.56 (95% CI: 0.39 to 0.82, p = 0.0026). A multivariate analysis was performed for age, gender, ECOG performance status, insurance status, BMI, PDL1 status and smoking history, amongst other variables. Worse survival outcomes were noted with an ECOG performance status ≥ 2, no history of smoking, and involvement of palliative care. Multivariable logistic regression analysis showed that PDL-1 expression > 50% was the only predictor of developing an irAE. Of note, receipt of ChT in combination with pembrolizumab compared to pembrolizumab alone did not predict for development of irAE. Conclusions: Development of irAEs was associated with doubling of PFS and OS, regardless of whether the ICI was administered alone or in combination with ChT. The differences were statistically significant regardless of age, gender, race, BMI, insurance status or performance status. Our study highlights the correlation between development of irAEs and improved survival outcomes in advanced NSCLC patients treated with ICIs.

e18683 Background: Cancer-directed therapy, including cytotoxic chemotherapy and immunotherapy, is a known risk factor for decreased SARS-CoV-2 seroconversion after vaccination, as a result of impaired viral immunity. Outcomes of COVID-19 infection are worse in patients on active treatment, especially those with hematologic malignancies or undergoing stem cell transplantation. The association between cancer subtypes and seroconversion rates is not well established. The goal of this study was to investigate predictive factors for SARS CoV-2 seroconversion and infection. Methods: We reviewed the electronic medical records of all patients with documented SARS CoV-2 antibody levels (between 7/2020-8/2021) in one of the largest integrated health systems in Pennsylvania. Patients who had a diagnosis of hematologic or solid malignancy, were on active treatment (including adjuvant), and had received ≥1 dose of an FDA authorized SARS CoV-2 vaccine were included. Data regarding SARS CoV-2 serology, vaccination, cancer history, and treatment regimens for each patient were collected systematically. Positive serology (reflecting seroconversion) was defined as any value ≥0.8 units/mL. Logistic regression analyses were used to examine predictors of seroconversion. Data was analyzed using SPSS v26 (IBM Corp). Results: A total of 292 patients met the inclusion criteria. Hematologic malignancy was present in 80.5% of the patients and solid tumors in 26.7%. Active disease was present in 71.6% of the cohort. Two vaccine doses were given to 92.5% of the patients and 54.8% of patients received a booster dose (95.2% received mRNA vaccines, either BNT162b2 (Pfizer BioNTech) or mRNA-1273 (Moderna)). A history of COVID-19 infection was present in 15.1% of patients, 59.1% of whom were seropositive. Rates of seroconversion were equivalent in those who received the BNT162b2 (70.2%) or mRNA-1273 (70.9%) vaccines. Seroconversion rates were 69.9% in those with active disease, 81.9% without evidence of disease, and varied by diagnosis as follows (indolent B-cell lymphoma 73.3%, aggressive B-cell lymphoma (BCL) 55.9%, plasma cell dyscrasia 80.1%, CLL 39.5%, myeloid disorder 90.2%, lung cancer 80%, breast cancer 80%, GI cancers 81.3%, and GU cancers 76.9%). On univariate regression, receipt of treatment for CLL (OR 5.79, 95% CI 2.92-11.48, p < 0.001) and aggressive BCL (OR 2.44, 95% CI 1.17-5.09) were predictive of negative serology. Results were not changed on multivariate regression when adjusted for age and active treatment. Conclusions: In this retrospective cohort of vaccinated patients on cancer-directed therapy, treatment for aggressive BCL and CLL was associated with negative seroconversion. In addition, more breakthrough infections occurred in seropositive patients, suggestive of underlying immunodeficiency related to treatment or decreased vaccine efficacy despite formation of virus-specific antibodies.