Distinct Mechanisms of Mismatch-Repair Deficiency Delineate Two Modes of Response to Anti-PD-1 Immunotherapy in Endometrial Carcinoma

Mismatch repair-deficient (MMRd) cancers have varied responses to immune-checkpoint blockade (ICB). We conducted a phase II clinical trial of the PD-1 inhibitor pembrolizumab in 24 patients with MMRd endometrial cancer (NCT02899793). Patients with mutational MMRd tumors (6 patients) had higher response rates and longer survival than those with epigenetic MMRd tumors (18 patients). Mutation burden was higher in tumors with mutational MMRd compared with epigenetic MMRd; however, within each category of MMRd, mutation burden was not correlated with ICB response. Pretreatment JAK1 mutations were not associated with primary resistance to pembrolizumab. Longitudinal single-cell RNA-seq of circulating immune cells revealed contrasting modes of antitumor immunity for mutational versus epigenetic MMRd cancers. Whereas effector CD8+ T cells correlated with regression of mutational MMRd tumors, activated CD16+ NK cells were associated with ICB-responsive epigenetic MMRd tumors. These data highlight the interplay between tumor-intrinsic and tumor-extrinsic factors that influence ICB response.

SIGNIFICANCE

The molecular mechanism of MMRd is associated with response to anti-PD-1 immunotherapy in endometrial carcinoma. Tumors with epigenetic MMRd or mutational MMRd are correlated with NK cell or CD8+ T cell-driven immunity, respectively. Classifying tumors by the mechanism of MMRd may inform clinical decision-making regarding cancer immunotherapy. This article is highlighted in the In This Issue feature, p. 247.

Ultrastructure of electrophysiologically identified human sinoatrial nodes

The ultrastructure of freshly excised human sinus node tissue was studied. In three female patients (ages 20, 30, and 36 years) medically refractory disabling episodes of inappropriate sinus tachycardia were surgically treated by extirpation of the sinus node. Each patient underwent intraoperative electrophysiological mapping to determine the area of earliest atrial activation. This area corresponded anatomically to the region of the sinoatrial node and was excised in each patient, the defect repaired using a pericardial patch. The freshly excised SA nodes underwent ultrastructural study. Three types of myocardial cells were identified: pacemaker or polygonal cells with clear cytoplasm, few mitochondria and sparse numbers of contractile elements (P cells); a transitional cell with slightly increased numbers of myofibrils (T cells); and typical atrial myocardial cells with normal numbers of contractile elements. These cell types have previously been identified in post-mortem studies of presumed SA node. The current study confirms the cell types in electrophysiologically documented SA nodes. The one abnormal finding observed in transitional cells in all patients was an increased number of lipofuscin-laden vacuoles. These vacuoles are considered a sign of cell degeneration and their occurrence was totally unexpected in these young adults. In summary, ultrastructural study of electrophysiologically documented human SA nodes confirmed the cell types identified in post-mortem studies. Furthermore, lipofuscin-laden vacuoles were increased in these three patients and this finding may serve as an ultrastructural marker associated with the syndrome of inappropriate sinus tachycardia.

Tep22, a novel testicular expressed gene, is involved in the biogenesis of the acrosome and the midpiece of the sperm tail

To identify new genes that could be involved in the differentiation and function of male germ cells, we have screened a murine testis cDNA library and isolated a clone that was named Tep22. The gene encoding Tep22 consists of three exons and is localized in the telomeric region of mouse chromosome 12. Expression analyses with RNA from different adult tissues revealed that Tep22 is predominantly expressed in spermatocytes and spermatids of the murine testis. Four Tep22 transcript sizes ranging from 647 to 1122 nucleotides were detected in testes of 15-day-old mice due to variable 5' UTRs, while the open reading frame of Tep22 has a length of 567bp in all transcript forms. Specific antibodies against Tep22 detected an approximately 22kDa band in testicular protein extracts, which was first observed in 18-day-old mice, indicating that Tep22 is translationally repressed for several days. Indirect immunofluorescence and immunoelectron microscopy experiments demonstrate that Tep22 is localized in the acrosomal region of early elongating spermatids, while the surrounding cytoplasm is barely labeled. During further germ cell development, the intensity of the staining in the acrosomal region decreases and is no longer detectable in late stages of elongating spermatids, whereas the amount of the Tep22 protein increases in the cytoplasm. Finally, Tep22 is incorporated into the midpiece of spermatids and is also present in the mitochondrial sheath of mature spermatozoa. Taken together, our results suggest that Tep22 is involved in the biogenesis of the acrosome as well as in the function of the midpiece of murine spermatozoa.

Utility of next generation sequencing to unequivocally establish clonality in synchronous vs metastatic endometrial and ovarian carcinomas

Background

Synchronous endometrial and ovarian carcinomas represent up to 10% of all endometrial and ovarian tumors. These are diagnostically challenging cases to determine if they represent dual primary tumors or related metastatic tumors.

Case

A 48-year-old was diagnosed with synchronous primary ovarian and endometrial malignancies on pathology based on traditional morphological parameters. However, following next generation sequencing (NGS) of tumors from both the uterus and ovary, the malignancies were unequivocally recognized as primary uterine tumor metastatic to the ovary using mismatch repair protein expression profile and tumor clonality.

Conclusion

NGS using FDA-approved commercially available platforms is becoming increasingly utilized to understand the genetic landscape of tumors and select the appropriate targeted therapies for improved outcomes. Simultaneous sequencing of synchronous endometrial and ovarian carcinomas may represent the new gold standard to unequivocally demonstrate tumor clonal relationships, properly classify disease as well as guide the most appropriate adjuvant treatment in these challenging cases.