Remembering Enzo Cerundolo

In January of 2020, the worldwide community of T cell immunologists lost one of our most respected leaders, Vincenzo ‘Enzo’ Cerundolo, FRS, to a much too early death from cancer. Only three months prior, Enzo stood on the stage of the Mathematics Institute at Oxford University, where he co-hosted the EMBO International Workshop on CD1 and MR1. Key findings of this wildly successful meeting are summarized in 14 focused scientific reviews. Here, I remember Enzo as a scientist and as a much beloved human being, highlighting his original scientific observations and unique leadership qualities.

While a fellow in Alain Townsend’s lab, Enzo reported a foundational observation of MHC class I antigen display to T cells in May of 1990 (1). Working with the now famous 221.174 B cell lines, known as T1 and T2, Enzo observed that that an 11-residue peptide from the influenza matrix protein, but not live virus encoding the full-length protein, could rescue MHC class I surface expression and T cell activation. Although the experimental outcome was clear, its meaning was not obvious. The authors wrote that all findings could be explained if ‘Class I assembly and transport is facilitated by association with peptides derived from intracellular antigens.’ Rescue occurred on endo H sensitive proteins, implying that ‘peptide acts on A2 heavy chains before their entry into the Golgi apparatus.’ The authors concluded that the block in T cells might be ‘due to the loss of transport of peptides from the cytosol.’ They were right on all three counts. These observations, as well as Enzo’s data mapping the missing factor to chromosome 6 (1), set the stage for the discovery of MHC encoded ‘transporter associated with antigen processing’ (TAP) genes (2–5). TAP genes allow cytosolic peptides to slip through transmembrane channels to load onto Class I in the endoplasmic reticulum. Combined, these findings explain in a general way how the cellular immune system can see otherwise hidden viral and self antigens derived from the cytosol.

More generally, understanding how small peptide antigens are generated from full length proteins is the basis for epitope mapping, the fundamental tool needed for design and evaluation of modern vaccines against pathogens and cancer, as well as tracking of T cell responses in disease with tetramers (6). Enzo mapped peptide antigens from melanoma cells in his own laboratory at Oxford (7, 8). His group made key observations in understanding T cell responses to cancer cells as part of his work with Cancer Research UK, the Cancer Research Institute and Ludwig Cancer Research (9). Previously viewed as a longshot approach to cancer therapy, T cell immunotherapy against cancer has shown spectacular results that are now widely recognized (www.nobelprize.org/prizes/medicine/2018/summary/).

I met Enzo for the first time in 2002 near the stage at the old auditorium of the Wood’s Hole Oceanographic Institute. I clearly remember this first encounter because Enzo had strong and attentive personal presence, as well as important data to share. Working with Stephan Gadola and Yvonne Jones, Enzo had published landmark work on the co-crystal of CD1b bound to phosphatidylinositol (PI) and two unnamed lipids (10). This manuscript described the first structure of the CD1b antigen presenting molecule, and it nucleated many research directions. Unexpectedly, the CD1b cleft was much larger than that of CD1d (11), and it contained extra pockets and tunnels, so it is a ‘maze for alkyl chains.’ The large cleft size and escape channels explained how CD1b could present mycolyl lipid antigens that were nearly twice the size of antigens presented by other CD1 proteins (12, 13). The unexpected identification of three, rather than one lipid ligand(s) in the cleft spawned a line of work to identify scaffold and spacer lipids that bind as chaperones alongside lipid antigens (14, 15).

Most importantly, this was the first solved CD1-lipid complex, providing foundation information for the mechanism of lipid antigen display. The CD1b-phospatidylinositol structure showed how alkyl chains insert inside CD1 to present the phosphoinositol group on the outside of CD1 as an epitope. Thus, Enzo’s work defined the basis for epitope mapping of both peptide and lipid antigens.

Cerundolo and Jones went on to solve the first structure of human CD1d (16). Understanding the size and shape of the CD1d cleft supported the development of synthetic glycolipid agonists for NKT cells (17, 18) as adjuvants. This structure also provided a surprise: CD1d could fold with and without a defined lipid ligand in the cleft. Concurrently with the Kronenberg (19) and Bendelac (20) groups, Enzo’s lab generated working CD1d tetramers that carried glycolipids exposing carbohydrate epitopes for T cell receptors (21). Enzo also warned the field that deletion of lipid synthases can cause lipid storage in addition to the loss of lipid-focused immune response (22).

Along with these many discoveries, Enzo built our field through his personal leadership qualities. Scientists wanted to work with Enzo -- he was invited to co-organize major CD1 workshops on both sides of the English Channel, in Tours in 2013 and in Oxford in 2019. Enzo was also active in the ‘conventional’ peptide Antigen Processing and Presentation workshops held every other year. Enzo strongly supported the developement younger scientists in the field. Under Enzo’s leadership, the Oxford CD1-MR1 Conference strongly highlighted the work of talented, newly independent investigators, who are well represented among the authors of this special issue.

For the last decade of his life, Enzo’s professional project was to lead the MRC Human Immunology Unit (HIU) of the MRC Weatherall Institute of Molecular Medicine (WIMM). The HIU has achieved worldwide influence by carrying out the difficult work of studying disease relevant questions in humans with experimental design that rigorously tests causal connections. Consider the ambition of an oral challenge study with live S. Typhi given to human volunteers, where Napolitani and Cerundolo identified peptide epitopes that dominate during a controlled infection with a natural pathogen (23).

As a visiting professor, I watched a remarkable parade of leading scientists gratefully accept invitations to present at the WIMM. The scientific seminars were abundant and well attended, sometimes to overflowing, from across the Oxford community. The unusually engaged audience would ask questions during and after the scientific talks. Enzo personally promoted this sense of scientific engagement. As he told me, the trick is to plan scientific meetings in which everyone really wants to be there. He fostered a scientific environment with high rigor and warm camaraderie.

By sheer coincidence, scientific business took me to Oxford during the week in which Enzo was inducted as a Fellow of The Royal Society. Enzo was honored to sign the Charter Book and fascinated to think about the scientific heft of the cosignatories. Yet, in the evenings before and after the signing ceremony in London, he did not speak of his own professional milestones that were richly celebrated by others. Enzo was thinking about the future. He was most interested to discuss new discoveries in the lab, T cells, vaccines, CD1, antigens, his vaccine, his family from Lecce, my science, my family from Boston, as well as Lucy’s, Marco’s and Giulia’s plans.

Memories of this visit now distill in my mind the essence of Enzo’s success as an investigator, lab head, institute director, and as a warmly loved father and husband. He possessed the drive and innate curiosity that propelled him to world class scientific discovery, yet also the humility and an outward facing empathy to support and encourage others in every aspect of life. Enzo led others by creating a personal sphere of honesty, respect and scientific excitement. People wanted to be with and work with Enzo. His life was too short, but fantastically well lived. He is deeply missed by his colleagues, who dedicate this special issue to him.

Biography

Enzo Cerundolo punting on River Cherwell, Oxford, UK.