Elucidating a novel respiratory-mammary axis of T cell immunity

Breastfeeding is associated with immunological benefits that persist beyond infancy, including reduced risk of
respiratory infection. While these benefits are often attributed to immunoglobulins and antimicrobial compounds,
human milk is also rich in T cells whose function is unknown. A central goal of my research career is to elucidate
the protective function of breastmilk T cells against infant respiratory infection. To this end, I propose to
investigate the respiratory-mammary axis of cellular immunity and its role in the establishment, retention, and
response of tissue resident memory T cells (TRM) in the lactating breast. I hypothesize that i) maternal exposure
to respiratory infections results in priming of T cell populations that go on to seed TRM in both the breast and the
respiratory tract and ii) antigen exposure via saliva of the nursing infant drives persistence of TRM in the lactating
breast. I will use samples from a cohort of mother infant pairs, which includes breastmilk cells (BMC), nasal
mucosal cells (NMC), and peripheral blood mononuclear cells (PBMC). In Aim 1, I will investigate whether T cells
resident to the upper respiratory tract and lactating breast are derived from a shared cellular population by
defining the transcriptional and clonal overlap of T cells from BMC and NMC using single cell RNA sequencing
with paired T cell receptor (TCR)αβ sequencing. In Aim 2, I will evaluate the contribution of infant respiratory
infection and coinciding maternal and infant respiratory infection on the frequency and functional state of
breastmilk T cell subsets. To do this, I will enroll mother-infant pairs seeking care at Seattle Children’s Urgent
Care clinics with PCR-confirmed infant SARS-CoV-2 or influenza A. BMC from acute and convalescent
timepoints will be evaluated by high-parameter flow cytometry for T cell immunophenotyping. In Aim 3, I will
interrogate breastmilk antigen-specific TRM responses in the setting of maternal and infant respiratory syncytial
virus (RSV) infection. I will enroll mother-breastfed infant pairs who present to urgent care with PCR-confirmed
infant RSV infection in which i) both the mother and infant are infected with RSV or ii) only the infant is infected,
I will stimulate maternal BMC from these pairs (along with those from healthy controls) with an RSV peptide pool
and assess the frequency and phenotype of T cells expressing activation-induced markers (AIM) using flow
cytometry. These studies will elucidate the establishment, retention, and response of TRM in the lactating breast,
with relevance to future work to discern how these cells may protect against infant respiratory infection. The
proposed work will take place at Seattle Children’s Research Institute under the co-mentorship of Dr. Whitney
Harrington and Dr. Alexis Kaushansky. I have additionally recruited a scientific advisory committee who will
support my success in achieving the proposed aims; my short-term objectives of gaining skill/expertise in
mucosal T cell biology, human study design, and computational biology; and my transition to an independent
faculty position. In short, this award will empower me to achieve my long-term goal of leading a research program
focused on infection and immunity during pregnancy, post-partum, and infancy.

Grant Number: 1K99AI182458-01A1
NIH Institute/Center: NIH
Principal Investigator: Blair Armistead