Max Cooper

Max D. Cooper

Emory University School of Medicine

Jacques Miller

Jacques Miller

The Walter and Eliza Hall Institute of Medical Research

For their discovery of the two distinct classes of lymphocytes, B and T cells – a monumental achievement that provided the organizing principle of the adaptive immune system and launched the course of modern immunology

The 2019 Albert Lasker Basic Medical Research Award honors two scientists for discoveries that have launched the course of modern immunology. Max D. Cooper (Emory University School of Medicine) and Jacques Miller (Emeritus, The Walter and Eliza Hall Institute of Medical Research) identified two distinct classes of lymphocytes, B and T cells, a monumental achievement that provided the organizing principle of the adaptive immune system. This pioneering work has fueled a tremendous number of advances in basic and medical science, several of which have received previous recognition by Lasker Awards and Nobel Prizes, including those associated with monoclonal antibodies, generation of antibody diversity, MHC restriction for immune defense, antigen processing by dendritic cells, and checkpoint inhibition therapy for cancer.

When Miller began his research—around 1960—scientists had uncovered some features of the adaptive immune system, which protects our bodies from microbial invaders, underlies immunological memory, and distinguishes self from foreign tissue. They knew that antibodies, soluble proteins whose quantities surge after infection, perform jobs that differ from tasks that rely on live, intact cells such as rejection of transplanted grafts.

Key immune system activities were known to occur in the spleen and other lymphoid tissues. The thymus, in contrast, teemed with lymphocytes—cells thought by then to initiate immunological functions—but lymphocytes from the thymus could not transfer immune responses to other animals. Furthermore, removing the organ from adult animals exerted no harmful effects. The thymus, according to prevailing wisdom, was dispensable, an evolutionary relic.

From vestigial to invaluable

Miller had no inherent interest in this useless body part, but observations about mouse lymphocytic leukemia drew him toward it when he began his Ph.D. work at the Institute of Cancer Research, London. A recently discovered virus caused this cancer when administered at birth, but not later, and preliminary experiments suggested that it targeted the thymus. To test whether it could multiply only in the newborn thymus, Miller removed the organ in newborn mice and then injected the virus.

He didn’t have a chance to find out the answer.

The pups remained healthy at first, but after weaning, they developed diarrhea and began wasting away. They were deficient in blood, lymph node, and spleen lymphocytes—and also in plasma cells, which produce antibody. The animals mounted a poor antibody response after bacterial immunization. Moreover, they failed to reject skin transplanted from unrelated mice and even rats, as would animals with an intact immune system. Two-thirds of the mice died prematurely.

Neonatal thymectomy was crippling immune activities, Miller concluded. Soon after publication of his initial results, other groups reported similar findings from studies on rats and rabbits. Miller subsequently established that the thymus is sometimes essential in adult animals too—to replenish the immune system if it is damaged by irradiation.

The thymus, he reasoned, might make cells that circulate and gain immune capabilities, poised to attack foreign threats throughout the body. To test this idea, he implanted thymuses into neonatally thymectomized mice and then introduced skin from different donors. The animals rejected grafts from unrelated individuals, but tolerated them from the strain that furnished the thymus. The thymus therefore, was supplying immunological function. Furthermore, in the recipient’s spleen—where lymphocytes multiply after stimulation— a significant fraction of dividing cells came from the donor thymus. As Miller had conjectured, cells from the thymus could migrate and mature.

Miller published the work in 1961 and 1962, and he presented his results at several meetings. Many scientists initially resisted his interpretations, including leading immunologists such as Peter Medawar (1915-1987) and MacFarlane Burnet (1899-1985). How could a disposable organ serve a vital purpose?

The strongest specific objection was that the lab in which Miller worked was a converted horse stable. Perhaps it was crawling with pathogens that put the animals in a stressed state, and the thymectomy pushed them into immunosuppression.

To address this possibility, Miller went to the U.S. National Institutes of Health, the only place in the world that had germ-free mice at the time. He repeated the experiments with those animals and confirmed that neonatally thymectomized mice accept foreign skin grafts. The immunological effects mapped to thymus removal, not to a pre-weakened immune system.

Dual lineage defense

In the meantime, Cooper, a pediatrician, had become interested in conditions that make children unusually susceptible to infections and, in 1963, he joined the laboratory of the late Robert A. Good at the University of Minnesota Medical School to explore his ideas. Some of the syndromes seemed to represent discrete, isolated segments of the adaptive immune system. For instance, many children with Bruton type agammaglobulinemia make no detectable antibody, yet can perform cell-mediated immune tasks. Conversely, children with other immunodeficiency conditions display the opposite physiological signature.

Such observations suggested the existence of two distinct arms of adaptive immunity in humans. By this time, however, the prevailing model, derived from Miller’s and other animal studies, suggested that a single pathway leads from thymus-generated lymphocytes to plasma cells. In this scenario, lymphocytes emerge from the thymus and disseminate to other tissues, such as the spleen, where stimulation with foreign substances triggers some of them to become antibody factories. The single-pathway model did not easily square with the clinical observations, which showed that cell-mediated activities could wither without wiping out antibody production. If lymphocytes give rise to plasma cells, it was not straightforward to explain how plasma cells and their products could abound when lymphocytes were scarce.

Results published far from the immunology mainstream pointed toward the chicken as a way to resolve this conundrum. In 1956, the late Bruce Glick (then a graduate student at Ohio State University) had reported in the Journal of Poultry Science that removal of a lymphoid organ—the bursa of Fabricius— soon after hatching could subdue antibody production. Perhaps, Cooper reasoned, he could use the chicken to simulate the apparent split reflected in the human diseases and tease apart potential contributions of the bursa and the thymus.

Cooper’s initial attempts to eliminate thymus function by removing the chicken thymus yielded no effects, and he speculated that newly hatched chickens might carry thymus-derived cells that had escaped from their birthplace before hatching, thus obscuring defects that should, theoretically, result from thymectomy. To address this possibility, he removed the thymus or the bursa of Fabricius from newborn chickens and then irradiated the animals to destroy residual immune cells that might have been floating around the body. Then he let the animals recover.

Irradiated chickens without a bursa did not produce antibodies after injection with bacteria or a foreign protein, and they lacked plasma cells. Their thymuses developed normally and lymphocytes flourished. In contrast, irradiated chickens with no thymus had few lymphocytes, but more than half made antibodies when stimulated. Subsequent studies showed that these animals could not reject skin grafts normally or execute other cell-mediated immune reactions.

In 1965 and 1966, Cooper published these findings and proposed that the bursa of Fabricius is essential for antibody production and the thymus is essential for cell-mediated immune responses. The names of bursa- and thymus-derived cells eventually shrunk to B- and T-cells, respectively. The two-pathway model provided a new lens through which to view human immunodeficiency diseases and brought fresh insight to a vast range of basic and clinical issues (see Figure).

Stem cell illustration

Dual-armed defense system
Stem cells from blood-forming tissues such as spleen, bone marrow, and fetal liver mature along the T-cell (top) or the B-cell (bottom) lineage to form, respectively, the cell-mediated or antibody-based components of the adaptive immune system. Along the way, signals from each type of developing cell prompt maturation and specialization of the other. In birds, the bursa of Fabricius hosts early stages of B-cell generation and antibody diversification, whereas in mammals, analogous steps occur in the bone marrow.
Illustration: Cassio Lynm / © Amino Creative

Crosstalk power

Even if these findings extended to mammals, which possess no obvious bursa equivalent, they raised perplexing questions. For instance, thymectomy plus irradiation of chickens softened antibody output—and neonatal thymectomies in mice stymied it. The split between the two pathways was not clean.

Miller (having joined the faculty at The Walter and Eliza Hall Institute of Medical Research) and his Ph.D. student, Graham Mitchell, decided to probe how the thymus might influence antibody production in mice. After obliterating thymus activity, they introduced thymus-derived cells, genetically distinct bone marrow-derived cells, or both before provoking antibody manufacture.

Neither cell type on its own reconstituted antibody production in the spleen. Only animals that received cells derived from the thymus and bone marrow achieved this feat. A collaboration was occurring between the two cell types.

Additional experiments revealed that the bone marrow-derived cells were the ones that spit out antibody, but only with assistance from the thymus-derived cells. Not only had Miller demonstrated that the dual system operates in mammals as well as birds, he also had exposed what we now know as helper T cells. This work ignited an explosion of interest in lymphocyte interactions.

Although mouse bone marrow contained cells that could give rise to antibody producers, the bone marrow might have received them from elsewhere, so the search for the mammalian bursa equivalent continued. In 1974, Cooper in collaboration with Martin Raff and John Owen (University College London) as well as independent investigators in Melbourne and Geneva, established that mammalian B cell precursors are generated in the blood-forming tissues—the liver in the fetus and the bone marrow after birth. This finding dovetailed with previous work on antibody development by Cooper. He had shown that two classes of antibody, IgM and IgG, each known for specific activities, come from a single precursor B cell that switches from IgM to IgG production.

Many laboratories subsequently elucidated the details of the system that Miller and Cooper unveiled, which operates in all jawed vertebrates. Cooper (at the University of Alabama, Birmingham, and then Emory University School of Medicine) went on to discover that jawless vertebrates—represented by the lamprey and hagfish—deploy a similarly organized scheme to recognize a vast array of foreign molecules, but with molecules that are structurally unrelated to the antibodies and receptors used by B and T cells.

By delineating the adaptive immune system’s two major branches, each of which performs distinct functions, Cooper and Miller opened a new era of cellular immunology. Virtually all fundamental discoveries in the field over the last 50 years can be traced to their pioneering work. Moreover, their historic findings have powered novel therapeutic strategies that have harnessed immune cells and their products to combat a vast range of illnesses—from cancer to autoimmune disorders to immunodeficiency conditions and far beyond.

by Evelyn Strauss

Key Publications of Max D. Cooper

Cooper, M.D., Peterson, R.D.A., and Good, R.A. (1965). Delineation of the thymic and bursal lymphoid systems in the chicken. Nature. 205, 143-146.

Kincade, P.W., Lawton, A.R., Bockman, D.E., and Cooper, M.D. (1970). Suppression of immunoglobulin G synthesis as a result of antibody-mediated suppression of immunoglobulin M synthesis. Proc. Natl. Acad. Sci. USA. 67, 1918-1925.

Cooper, M.D., Lawton, A.R., and Bockman, D.E. (1971). Agammaglobulinaemia with B lymphocytes. Specific defect of plasma-cell differentiation. Lancet. 2, 791-794.

Owen, J.J.T., Cooper, M.D., and Raff, M.C. (1974). In vitro generation of B lymphocytes in mouse foetal liver – a mammalian “bursa equivalent”. Nature. 249, 361-363.

Pancer, Z., Amemiya, C.T., Ehrhardt, G.R.A., Ceitlin, J., Gartland, G.L., and Cooper, M.D. (2004). Somatic diversification of variable lymphocyte receptors in the agnathan sea lamprey. Nature. 430, 174-180.

Cooper, M.D. (2015). The early history of B cells. Nat. Rev. Immunol. 15, 191-197.

Key Publications of Jacques F.A.P. Miller

Miller, J.F.A.P. (1961). Immunological function of the thymus. Lancet. 2, 748-749.

Miller, J.F.A.P. (1962). Effect of neonatal thymectomy on the immunological responsiveness of the mouse. Proc. Roy. Soc. 156B, 410-428.

Miller, J.F.A.P. (1962). Immunological significance of the thymus of the adult mouse. Nature. 195, 1318-1319.

Miller, J.F.A.P., and Mitchell, G.F. (1968). Cell to cell interaction in the immune response. I. Hemolysin-forming cells in neonatally thymectomized mice reconstituted with thymus or thoracic duct lymphocytes. J. Exp. Med. 138, 801-820.

Miller, J.F.A.P. (2011). The golden anniversary of the thymus. Nat. Rev. Immunol. 11, 489-495.

Miller, J. (2019). How the thymus shaped immunology and beyond. Immunol. Cell Biol. 97, 299-304.

Perspectives on B and T Lympocytes

Watts, G. (2011). Jacques Miller: immunologist who discovered role of the thymus. Lancet. 178, 1290.

Gitlin, A.D., and Nussenzweig, M.C. (2015). Fifty years of B lymphocytes. Nature. 517, 139-141.

Seurat’s Dots: A Shot Heard ‘Round the Art World

Seurat’s Dots: A Shot Heard ‘Round the Art World

How the color theories of a chemist have ricocheted across centuries of artistic and scientific imagination.

Award presentation by Craig Thompson

In this ongoing era of molecular biology, it is easy to forget that the functional unit on which biology is built, is the cell. Working independently, the two exceptional scientists that we honor today discovered that the adaptive immune system is composed of two distinct cell types, B cells and T cells. Through their studies of lymphocyte development, Max Cooper and Jacques Miller have provided the framework on which modern immunology is built.

Miller and Cooper’s combined discoveries have also provided the foundation for most of today’s immune therapies. Monoclonal antibody production would not be possible without the antibody repertoire created and stored within the B cell lineage. One such antibody will be recognized with today’s Clinical Lasker Prize. Similarly, the success of T cell-based therapies, such as the recent development of CAR-T cells to treat cancer, depend on the immunologic properties that T cells acquire as they undergo lineage-specific development in the thymus.

The discovery of B and T cells also provided the foundation through which molecular biologists began to elucidate answers to the fundamental questions concerning how the immune repertoire is generated and how the immune system distinguishes self from non-self. The subsequent discoveries of V(D)J recombination, of dendritic cell antigen presentation, and of MHC-restriction of cell-mediated immunity have gone on to win recognition in the form of Lasker and Nobel prizes for providing the molecular details concerning how immune specificity is created and maintained. But none of these discoveries would have been possible without the immune framework involving the independent development of B and T cells discovered by Cooper and Miller.

So how did these two scientists discover that the adaptive immune system was composed of two independent but complementary cell types? When Cooper and Miller were starting their research careers in the early 1960s, antibodies were known to provide the protective immunity elicited by vaccines. Antibodies were produced during an immune response by terminally differentiated cells called plasma cells, but from where these cells arose was uncertain. The antibody theory of immunity was also recognized to be incomplete. Certain immunologic processes such as organ graft rejection did not appear to be result of antibody production. At the time that Cooper and Miller began, lymphocytes were considered a single cell type that originated in the spleen and lymph nodes and circulated throughout the body through the blood and lymphatics. The thymus, although known to contain lymphocytes, was considered an evolutionary remnant of no discernable significance. In fact, this matter was considered settled when it became routine, during the 1950s and 1960s, to remove the thymus during pediatric heart surgeries. Despite not having a thymus, these patients suffered no apparent immune consequences as they grew up.

It was Miller who first challenged the notion that the thymus was a vestigial organ. At the time, he was studying the factors that regulated the development of lymphocytic leukemia in mice. As part of his studies, he removed the thymus from mice at weaning and found that the incidence of viral and carcinogen-induced lymphocytic leukemia was dramatically reduced. He realized that this could be because either the thymus was the site of production of a humoral factor that contributed to lymphocytic leukemia or because the lymphocytes in the thymus were at a unique stage of development that rendered them susceptible to developing into a leukemia. To extend his studies, Miller decided to remove the thymus even earlier, at the time of birth, and then test the mice’s susceptibility to virally-induced leukemia. He never got to complete this experiment. Within weeks of weaning, the mice whose thymus was removed at birth developed a severe reduction in peripheral lymphocyte numbers, a systemic wasting syndrome, and an increase in opportunisitic infections. Today, we would recognize this constellation of symptoms as acquired immunodeficiency syndrome or AIDS, a disease that results from the loss of T cells. However, at the time, Miller’s results were completely unexpected. As Miller further characterized mice whose thymus was removed at birth, he found that they lacked the ability to reject foreign skin grafts, a hallmark of cell-mediated immunity, but they also displayed some defects in antibody production. This work established the thymus as an immunologic organ, critical for the development of cell-mediated immunity and apparently participating in the ability of animals to produce effective antibodies. Miller would over the next decade demonstrate that the thymus was the site of the development of T cells and helped to define the critical role of T cells in the successful generation of a cell-mediated immune response.

In contrast to T cells, the demonstration that B cells were a distinct lineage of immune cells did not result initially from studies in mice. Unique among vertebrates, birds were discovered to have a second thymus-like organ called the bursa of Fabricius. In the 1950s, Bruce Glick and his colleagues at Ohio State reported that when chickens had the bursa removed, their ability to produce antibodies was reduced, but other types of immune response were not examined. Shortly thereafter, Robert Good’s lab in Minnesota was undertaking experiments like Miller’s to understand the pathogenesis of lymphocytic leukemia in birds. In contrast to Miller’s results, removing the thymus in a chicken had no effects on the lymphocytic leukemia caused by avian leukosis virus. Instead, the group found that it was removing the bursa that reduced the incidence of leukemia. However, as they and others carried out more detailed immunologic analysis of chickens that had had either their thymus or bursa removed, the results proved highly variable. That is when Cooper enters our story.

It was Cooper who speculated that the variability resulted from the fact that when a chicken hatches, many lymphocytes had already completed their development in the thymus and bursa and could be observed seeding the peripheral lymphoid organs. To examine this possibility, Cooper eliminated the existing peripheral lymphocytes in newly hatched chicks through sublethal irradiation and then surgically removed the bursa of Fabricius or the thymus. The results were clear, the animals lacking a bursa failed to produce either plasma cells or antibodies and did not respond to an immunologic challenge with antibody production. In contrast, the chickens lacking a thymus had the same defects in cell-mediated immunity as those observed in the mice lacking a thymus reported by Miller. Based on this work, Cooper proposed that the adaptive immune system, was divided into two separate lymphoid lineages: the antibody producing lineage, derived in chickens from the bursa of Fabricius and named B cells, and the lineage responsible for cell-mediated immunity arising from the thymus and given the name T cells.

Even though mammals lacked a bursa of Fabricius, Cooper hypothesized that an equivalent mammalian B cell lineage must exist. He based his belief on the existence of human patients he was caring for who had a disease called Bruton’s agammaglobulinemia. Like Cooper’s bursectomized chickens, patients with Bruton’s agammaglobulinemia failed to produce plasma cells or antibodies but retained the ability to reject foreign tissue grafts.

In subsequent years, both Cooper and Miller played pivotal roles in identifying that B cells arise from hematopoietic stem cells in the liver and bone marrow in both birds and mammals. The rapid amplification of B cell numbers provided by subsequent development in the chicken bursa of Fabricius after hatching is apparently not needed in mammals. Instead it was found that the antibodies that protect newborn mammals from infection in the first 6 months of life come from maternal antibodies that cross the placenta in the third trimester of pregnancy.

Following their successful demonstration that B and T cells were independently produced during mammalian development, Miller and Cooper each extended their findings by demonstrating that many protective immune responses result from the independent development of specificity within the B and T cell lineages. They helped demonstrate that cooperation between these two arms of the lymphoid immune system were often required to mount a successful immune response and that it is the combined properties of B and T cells that provides us with lifelong immunity from foreign pathogens.

Please join me in giving a round of applause for this year’s winners of The Albert Lasker Basic Medical Research Award, Max Cooper and Jacques Miller, whose foundational discoveries, have informed and shaped the course of modern immunology.

Acceptance remarks

2019 Basic Award video