Domain: Immunology and Molecular Biology
Persona: Senior Principal Investigator and Chair of Immunology
Part 2: Summarize
Abstract:
This session features an in-depth professional retrospective and technical discussion with Dr. Leslie Berg, a preeminent figure in T cell biology and former President of the American Association of Immunologists (AAI). The dialogue traces Dr. Berg's trajectory from her doctoral work on bovine papilloma virus to her foundational postdoctoral contributions in the laboratory of Mark Davis, where she developed early T cell receptor (TCR) transgenic mouse models. The technical core of the discussion focuses on the "rheostat" model of TCR signaling, specifically how the Tec kinase ITK modulates signal strength to determine T cell fate—discriminating between positive and negative selection in the thymus and effector versus memory differentiation in the periphery. Dr. Berg highlights recent findings showing that while NFAT and MAPK pathways exhibit digital (all-or-none) activation, the NF-κB pathway is analog and highly sensitive to ITK activity. The conversation concludes with an analysis of the limitations of current CAR-T therapies regarding signaling uniformity and the strategic importance of departmental resources, such as embedded bioinformatics and grant-writing support, in sustaining modern academic research.
T Cell Signaling, Selection, and the Professional Trajectory of Leslie Berg
0:00 - Introduction to the Session: Cindy Lifer introduces Dr. Leslie Berg at the 2025 AAI Conference. Dr. Berg is recognized for her role in developing early TCR transgenic mice and her extensive leadership within the AAI and as a Department Chair at the University of Colorado.
2:24 - Transition from Viral Molecular Biology: Dr. Berg describes her PhD work at UC Berkeley on the bovine papilloma virus genome. Her transition to immunology was driven by the desire to apply molecular tools to complex "black box" biological systems in whole-animal models.
6:08 - The Stanford Postdoc and TCR Transgenics: Joining Mark Davis’s lab shortly after the cloning of the TCR, Dr. Berg was instrumental in creating early transgenic models. These models were designed to observe positive and negative selection in the thymus, providing a controlled environment where the majority of T cells shared a single receptor specificity.
8:42 - Kinase Specialization at Harvard: Dr. Berg attributes her focus on signaling to her time at Harvard, influenced by colleagues specializing in kinases (e.g., the discovery of Src as a tyrosine kinase). This led her to investigate the role of kinases like LCK and the identification of new T cell-specific tyrosine kinases.
9:41 - The Mystery of Thymic Selection: A central theme of Dr. Berg's research is the "signaling paradox": how the same TCR induces apoptosis (negative selection) upon strong signaling but promotes survival and maturation (positive selection) upon weak signaling.
11:19 - Professional Environment ("Seed and Soil"): Dr. Berg emphasizes that a scientist's research direction is profoundly shaped by their immediate colleagues. She notes that the "soil" (institutional environment) dictates which questions become prominent through daily technical and intellectual exchange.
18:05 - Mentorship Philosophy: Drawing from her PhD advisor, Mike Botchan, Dr. Berg advocates for a "rank-agnostic" approach to scientific data. Key takeaways include the necessity of being emotionally detached from hypotheses and the value of "failed" experiments as the primary drivers of new mechanistic insight.
26:51 - TCR Signal Strength and ITK: The discussion pivots to current research on how signal strength regulates T cell fate. Dr. Berg’s lab identifies ITK as a signaling amplifier or rheostat. While some pathways (NFAT, MAPK) trigger digitally, NF-κB activation is graded and contingent on ITK-mediated diacylglycerol (DAG) production.
29:00 - Mechanistic Insights for CAR-T Therapy: Current CAR-T constructs are criticized for being "unidimensional." Dr. Berg suggests that understanding the TCR's ability to produce heterogeneous fates (effector vs. memory) via varied signal strengths could lead to better CAR-T designs, potentially using multiple constructs to mimic natural T cell repertoire diversity.
39:26 - Leadership and Resource Allocation: As a Department Chair, Dr. Berg highlights the success of providing centralized "discretionary" resources. Key implementations include a dedicated bioinformatician and a grant-writing consultant to improve the technical clarity and success rates of faculty submissions.
42:48 - Historical Context and Close: A brief personal note on Dr. Berg’s background in Beverly Hills and her interactions with notable figures before concluding the session with a reminder of the AAI's role in supporting the immunology community.
Part 3: Reviewer Recommendation
Target Review Groups:
Molecular Immunologists: To evaluate the mechanistic data regarding ITK and its differential effects on NF-κB versus NFAT translocation.
Academic Clinical Oncologists (Cellular Therapy): To review the implications of TCR signaling "wiring" on the development of more persistent memory-phenotype CAR-T cells.
University Research Administrators/Deans: To analyze the "Colorado Model" of centralized departmental support (bioinformatics and grant consulting) as a method for improving faculty productivity and retention.