Background: Determinants of sensitivity and resistance to immune checkpoint inhibitors (ICIs) are poorly understood. An intact HLA class-I antigen presentation machinery (APM) is necessary for tumor-antigen recognition by effector T-cells and disruptions to the APM can cause ICI resistance. The peptide loading complex (PLC) is a multi-chaperone complex located in the endoplasmic reticulum in which tapasin (Tap), calreticulin (CalR) and ERp57 play major roles. The PLC allows for optimal peptide selection and loading onto HLA class-I heavy chain and is critical for adequate cell surface presentation of peptide-HLA complexes. We studied the frequency and clinical significance of cancer-cell selective PLC protein defects in human NSCLC. Methods: Multiplex quantitative immunofluorescence (mQIF) was performed to simultaneously and spatially measure cytokeratin (CK), Tap, CalR, ERp57 and CD8 protein levels in 1,031 primary NSCLCs from 5 independent cohorts represented in tissue microarrays. The protein levels were measured in CK-positive cancer-cells and in CK-negative stromal cells. The presence of lower marker levels in malignant cells relative to stromal cells within the same sample was considered as cancer-cell selective downregulation. Cohorts #1-3 included baseline samples from patients treated without ICIs and Cohort #4 included samples from patients treated with ICIs. Cohort #5 contained lung adenocarcinomas clinically tested for EGFR and KRAS mutations. The association between the levels of Tap, CalR and ERp57, their association with clinicopathologic variables, CD8+ T-cell levels and outcomes were studied. Results: mQIF analysis identified cancer-cell selective downregulation of Tap, CalR and/or ERp57 in 73%, 81%, 68% and 75% of cases from Cohorts #1-4, respectively. The most common PLC alterations were cancer-cell downregulation of Tap alone in Cohorts #1 (32%), #3 (34%) and #4 (36%); and Tap-CalR in Cohort #2 (29%). Tap and ERp57 levels were significantly higher in stage IV than in earlier stage tumors. The PLC marker levels and the frequency of cancer-cell selective downregulation were comparable across EGFR and KRAS mutated samples. NSCLCs with cancer-cell Tap downregulation had lower CD8+ T-cell infiltration and shorter OS across all cohorts that reached statistical significance in Cohort #4 (median OS 12.08 vs 21.00, HR=1.72, 95% CI 1.02-2.89, p=0.034). The cancer-cell selective downregulation of CalR was associated with shorter OS in cohorts #1 and #3. Conclusions: HLA class-I PLC components show variable levels in treatment naïve NSCLCs. Downregulation of Tap in cancer-cells, alone or in combination with other PLC members occurs in up to 60% of cases and is associated with reduced CD8+ TILs and shorter OS preferentially in patients treated with ICIs. Cancer-cell Tap downregulation could mediate primary ICI resistance and has biomarker potential.