Understanding the mechanisms mediating the abrupt accumulation of regulatory T cells into neonatal skin which are responsible for establishing tolerance to skin commensal microbes.

1. Commensal microbes and hair follicles
coordinately drive Treg migration
into neonatal skin
Tiffany Scharschmidt, M.D.
Assistant Professor
Department of Dermatology
University of California, San Francisco

2. How do host and commensals cooperate early in life to promote
immune tolerance and a healthy symbiotic relationship?
Neonatal Life
Images adapted from Tamburini et al. Nat Med (2016)

3. Scharschmidt et al. Immunity (2015)
Tolerance to skin commensals is preferentially established in neonatal life
Neonatal skin Tregs are required to establish tolerance
A wave of Tregs into neonatal skin mediates tolerance to commensals
S. epidermidis
+ Immune
Tolerance
S. epidermidis
+
Failure to
establish
tolerance
Critical window

4. What drives migration of Tregs into neonatal skin?

5. This is a busy time for skin…
HF
HF HF
Hair follicle morphogenesis
Day 6
Day 13
Neonatal Tregs
localize to hair follicles
Microbial Colonization
Belkaid & Naik. Nat Imm (2013)
Day 13 FoxP3

6. Hypothesis: Chemokine(s) produced by developing hair
follicles direct Treg migration into neonatal skin and
commensal microbes augment this process.

7. Does hair follicle morphogenesis drive accumulation of
Tregs in neonatal skin?

8. K5/Dkk1 neonates have disrupted HF development and fewer skin Tregs

9. Do commensal microbes drive accumulation of
Tregs in neonatal skin?

10. Treg accumulation is significantly and preferentially reduced
in germ-free neonates

11. What are the molecular mechanisms that
mediate accumulation of Tregs in neonatal skin?

12. Combined discovery approach to identify chemokine-receptors
pairs mediating neonatal skin Treg accumulation
RNAseq D13 Skin vs. LN TregsChemokine qPCR array D6 vs. D13 skin
Receptors on neonatal skin TregsSkin chemokines expressed in this window
Chemokine qPCR array D13 SPF vs. GF skin
Skin chemokines augmented by commensals
Ccl20/Ccr6

13. Commensals augment expression of Ccl20 in developing HFs
D13 SPF
Ccl20 reduced
in GF skin
RNA in situ hybrid. shows
Ccl20 in HF keratinocytes
Do neonatal skin Tregs express cognate receptor CCR6?

14. Ccr6 is preferentially expressed by neonatal skin Tregs

15. Can Ccl20/Ccr6 drive neonatal Treg migration?

16. Ccl20 preferentially drives neonatal Tregs migration in vitro
D10 Thymic CD4+
Chemokine
3h
Analyze flow-through to assess Treg migration

17. Ccr6promotes skin Treg accumulation in neonatal adoptive transfer
i.p. injection
1.5M CD45.1 WT
CD4+ thymocytes
D9 rag2-/-
Harvest skin, SDLN, spleen
2wk post-transfer
1.5M CD45.2 Ccr6-/-
CD4+ thymocytes
Gated on
CD4+ FoxP3+

18. Hair Follicle
Development
Commensals and developing HFs coordinately direct Tregs to skin
during the optimal window for commensal-specific tolerance

19. How do specific commensals and
commensal products shape the hair follicle
immune environment?

20. Acknowledgments
Mentors
Michael Rosenblum
Michael Fischbach
Abul Abbas
Scharschmidt Lab
Kimberly Vasquez
Elizabeth Leitner
Kevin Chu
Rosenblum Lab
Mariela Pauli
Niwa Ali
Maggie Lowe
Collaborators
Justin Sonnenburg (Stanford)
Sarah Millar (Upenn)
James Moon (MGH)
Elizabeth Grice (UPenn)
Michael Otto (NIH)
Jan Liese (Germany)
Funding
scharschmidtlab.ucsf.edu