A Short History of Immunosuppressants And The Woman Who Invented Them

I’ve been thinking about the field of experimental transplantation research lately. There has been great research in this area recently, including work in Circulation Research on using nanoparticles to target potent immunosuppressants to key areas to suppress rejection (Bahmani, Uehara et al. 2018). There was also an interesting paper that used an aortic arch transplant model to study regression of atherosclerosis published in ATVB (Li, Luehmann et al. 2018). I began thinking about transplantation and the issue of acute rejection. There is also the problem of longer-term chronic vasculopathy and remodeling, but how did the field get over the first hurdle of acute rejection? It’s so fundamental to all organ transplantation that takes place in the clinic today. I decided to look into how we got to where we are today.

I found out that one of the earliest immunosuppressive agents was 6-mercaptopurine (6-MP). 6-MP was developed by a chemist named Gertrude Elion. I was delighted to find out that a woman developed this drug, especially as it was recently Women in Science Day on February 11th. Elion was born in New York City and earned a Bachelor’s degree at Hunter College and a Master’s degree in chemistry at NYU. She submitted 15 applications for graduate fellowships which were all turned down, leading her to enroll in secretarial school. She moved through several other jobs before working in as an assistant at what is now GlaxoSmithKline (GSK). While working there, she began earning her doctorate at night but stopped due to the difficulty of the commute. It was at GSK that Elion developed 6-MP, but she was only getting started.

6-MP was first used in the late 1950’s as chemotherapy to suppress antibody formation in pediatric cancer which improved survival from 3-4 months up to 12 months. 6-MP was next used in rabbits that were injected with bovine serum albumin to stimulate a powerful antigen response, but 6-MP prevented it (Schwartz, Stack et al. 1958). Next, a British surgeon, Roy Calne wanted to test whether 6-MP’s immune suppression could be used to prevent rejection after a transplant. He treated a dog with 6-MP and then transplanted a kidney from another dog. Ordinarily, the recipient dog’s immune system would attack the new kidney as if it were an invader. The kidney in the 6-MP treated dog survived 44 days compared to only 10-days for dogs that weren’t given 6-MP (Calne 1960). This drug seemed promising, but it had a high risk of toxicity, and this is where the story gets interesting.

Roy Calne wanted to find a drug that was as effective as 6-MP but less toxic, so he asked Gertrude Elion. Elion suggested another compound that she had recently synthesized, which was azathioprine (AZA) (Elion, Callahan et al. 1960). Clinicians will be familiar with this drug, but as a PhD scientist, I had never heard of it before now (and I did my PhD in pharmacology, but don’t hold it against me). AZA is a pro-drug that that is activated by glutathione in red blood cells to produce the active metabolite 6-MP in plasma. AZA was not only superior to 6-MP for preventing alloimmune transplant rejection, it was far less toxic. In 1962, only 2 years after the kidney transplant study with dogs, AZA was being used in human kidney transplants together with prednisone (Murray, Merrill et al. 1963). From this point onward, kidney transplants using Gertrude Elion’s AZA compound skyrocketed.

In 1988, Gertrude Elion was awarded the Nobel Prize in Physiology or Medicine, just the 5th woman to receive the award at the time. The development of AZA and more importantly, its use as an immunosuppressive agent allowed for the transplantation of many other organs, including livers, lungs, and hearts (Elion 1989). Other immunosuppressants have been developed which are in use for heart transplantation today but AZA is still being used for kidney transplants and chronic inflammatory diseases like rheumatoid arthritis and Crohn’s disease. Elion’s AZA is also listed as an essential medicine by the World Health Organization.

Gertrude Elion was an amazing scientist that had an enormous impact on health across the world. In addition to the synthesis and development of AZA, she is credited with the synthesis of allopurinol to treat gout and ancyclovir to treat herpes simplex virus. Both of these drugs are classified as essential medicines by the WHO. Her knowledge of both chemical synthesis and the biochemical basis of disease set her apart as a truly remarkable scientist who overcame many obstacles that women in science still face. Gertrude Elion should serve as a role model for anyone interested in science.



“Gertrude B. Elion.” https://en.wikipedia.org/wiki/Gertrude_B._Elion

“Gertrude B. Elion Biographical.” https://www.nobelprize.org/prizes/medicine/1988/elion/biographical/

Bahmani, B., M. Uehara, L. Jiang, F. Ordikhani, N. Banouni, T. Ichimura, Z. Solhjou, G. J. Furtmuller, G. Brandacher, D. Alvarez, U. H. von Andrian, K. Uchimura, Q. Xu, I. Vohra, O. A. Yilmam, Y. Haik, J. Azzi, V. Kasinath, J. S. Bromberg, M. M. McGrath and R. Abdi (2018). “Targeted delivery of immune therapeutics to lymph nodes prolongs cardiac allograft survival.” J Clin Invest 128(11): 4770-4786.

Calne, R. Y. (1960). “The rejection of renal homografts. Inhibition in dogs by 6-mercaptopurine.” Lancet 1(7121): 417-418.

Elion, G. B. (1989). “The purine path to chemotherapy.” Science 244(4900): 41-47.

Elion, G. B., S. W. Callahan, G. H. Hitchings and R. W. Rundles (1960). “The metabolism of 2-amino-6-[(1-methyl-4-nitro-5-imidazolyl)thio]purine (B.W. 57-323) in man.” Cancer Chemother Rep 8: 47-52.

Li, W., H. P. Luehmann, H. M. Hsiao, S. Tanaka, R. Higashikubo, J. M. Gauthier, D. Sultan, K. J. Lavine, S. L. Brody, A. E. Gelman, R. J. Gropler, Y. Liu and D. Kreisel (2018). “Visualization of Monocytic Cells in Regressing Atherosclerotic Plaques by Intravital 2-Photon and Positron Emission Tomography-Based Imaging-Brief Report.” Arterioscler Thromb Vasc Biol 38(5): 1030-1036.

Murray, J. E., J. P. Merrill, J. H. Harrison, R. E. Wilson and G. J. Dammin (1963). “Prolonged survival of human-kidney homografts by immunosuppressive drug therapy.” N Engl J Med 268: 1315-1323.

Schwartz, R., J. Stack and W. Dameshek (1958). “Effect of 6-mercaptopurine on antibody production.” Proc Soc Exp Biol Med 99(1): 164-167.



Turning Back The CLOCK: A Look Into The History of Circadian Oscillations

As an early career researcher, I feel that I lack some critical background knowledge of foundational studies and scientists in research. Most of my blog posts will focus on recent papers or topics, and I’ll dig into the history of that topic to find out how we got to where we are.

Many fantastic papers have been published on the circadian clock lately. Drs. David Montaigne and Bart Staels recently published a Viewpoint on the topic of the circadian clock and cardiovascular disease in Circulation Research.1 My basic understanding of the circadian clock is that transcription factors, CLOCK and BMAL1, are critical proteins. Light is sensed at the retina and the optic nerve transmits a signal to the suprachiasmatic nuclei then throughout the body. Since light (historically) came from the sun, these proteins and the clock functions generally oscillate with day and night. Knocking out or mutating clock proteins can alter metabolism, immunity, and a slew of other systems.

A 2013 paper published in Circulation by Xiaoyue Pan and colleagues showed increased atherosclerosis in mice where the CLOCK protein was mutated, thus disrupting the circadian rhythm.2 The mechanisms appeared to be elevated ApoB48 particles and increased macrophage cholesterol scavenging. In 2009, a Circulation paper by Ciprian Anea and colleagues showed increased collagen deposition and fibrotic remodeling after arterial ligation in the carotid artery of BMAL1 knockout mice.3 Finally, a 2018 Cell Metabolism paper by Carla Winter showed that myeloid cells behave in a circadian fashion.4 These are impressive recent papers, but how did we get to this point? I wanted to gain a better understanding of where the science of biological clocks began.

My first stop was the “circadian clock” page on Wikipedia, but it was lacking any historical context.5 Next, I found a review on Pubmed from 1993 by a scientist named Colin Pittendrigh in the Annual Review of Physiology entitled, Temporal organization: reflections of a Darwinian clock-watcher.6 This review was more of an autobiography than review, but it was a joy to read. I would suggest reading the entire review, but I’m going to summarize some it here. After reading a few paragraphs it became evident that Colin Pittendrigh might be a prominent figure in the science of biological clocks. I did a quick search (the Wikipedia page for “Colin Pittendrigh”) and found this in the second sentence, “…father of the biological clock…”, which came from a Stanford press release upon Pittendrigh’s death.7,8

What I found in Pittendrigh’s 1993 “reflections” was that he was an extraordinary scientist, and an interesting man. Pittendrigh begins by recounting how he became interested in biology. Living in the north of England, he kicked a soccer ball through the window of the town hall and needed to replace it. Needing money, he entered a contest for the best wild flower collection from the local Boy Scouts and won. This sparked his biological interest. During high school, Pittendrigh discovered Charles Darwin’s works which greatly influenced him. He says that his Darwinian beliefs later survived exposure to Lamarckian convictions of a college professor. During wartime in the 1940s, he was in Trinidad and was instructed to focus on breeding vegetables for the campaign. Later, he studied Malaria by focusing on habits of mosquitoes, and eventually he studied drosophila behavior. During these experiences, he observed periodicity in the behaviors of these organisms.6

With influences from colleagues, Pittendrigh reasoned that the biological clock must be endogenous.6 During his time at Princeton and Stanford, Pittendrigh published many papers including five in the journal, Science. Almost all of these were published on the circadian oscillations of plants and animals; however, he had other interests, as well. Notably, a 1965 Science paper titled, Proposed Biological Exploration of Mars between 1969 and 1973.9 Pittendrigh’s career in science was monumental, although he didn’t discover the proteins involved in biological clocks. The CLOCK protein was discovered in 1993 and BMAL1 was discovered in 1997, the year after Pittendrigh’s death.10,11 These discoveries undoubtedly wouldn’t have been made without the pioneering work of Colin Pittendrigh.

Dr. Pittendrigh’s life and discoveries are remarkable and in his writing, he constantly references others that were instrumental to his ideas and discoveries. With mounting pressure to have first or last author publications in our time (forgive the pun), it is easy to overlook others who make scientific progress possible. And although Colin Pittendrigh did not study cardiovascular diseases, his findings are having an impact on cardiovascular medicine now. This highlights the interdisciplinary nature of science and how ideas from diverse fields impacts others. It is always beneficial to read papers, attend seminars, and speak with colleagues from diverse fields to broaden our own experimental approaches and ideas.



  1. David Montaigne & Bart Staels. Time to Check the Clock in Cardiovascular Research and Medicine. Circulation Research. 2018; 123:648–650
  2. Xiaoyue Pan, Xian-Cheng Jiang, and M. Mahmood Hussain. Circulation. 2013 Oct 15; 128(16): 1758–1769.
  3. Anea CB, Zhang M, Stepp DW, Simkins GB, Reed G, Fulton DJ, Rudic RD. Circulation. 2009 Mar 24;119(11):1510-7
  4. Winter C, Silvestre-Roig C, Ortega-Gomez A, Lemnitzer P, Poelman H, Schumski A, Winter J, Drechsler M, de Jong R, Immler R, Sperandio M, Hristov M, Zeller T, Nicolaes GAF, Weber C, Viola JR, Hidalgo A, Scheiermann C, Soehnlein O. Cell Metab. 2018 Jul 3;28(1):175-182.e5
  5. https://en.wikipedia.org/wiki/Circadian_clock
  6. S. Pittendrigh. Temporal organization: reflections of a Darwinian clock-watcher. Annu. Rev. Physiol. 55, 17 16-54. 1993.
  7. https://en.wikipedia.org/wiki/Colin_Pittendrigh
  8. Stanford University News Service. https://news.stanford.edu/pr/96/960325pittendrig.html 1996.
  9. Pittendrigh CS. Proposed Biological Exploration of Mars between 1969 and 1973. Science. 1965 Apr 30;148(3670):667.
  10. King DP, Zhao Y, Sangoram AM, Wilsbacher LD, Tanaka M, Antoch MP, Steeves TD, Vitaterna MH, Kornhauser JM, Lowrey PL, Turek FW, Takahashi JS. Positional cloning of the mouse circadian clock gene. Cell. 1997 May 16;89(4):641-53.
  11. Hogenesch JB, Chan WK, Jackiw VH, Brown RC, Gu YZ, Pray-Grant M, Perdew GH, Bradfield CA (March 1997). “Characterization of a subset of the basic-helix-loop-helix-PAS superfamily that interacts with components of the dioxin signaling pathway”. The Journal of Biological Chemistry. 272 (13): 8581–93.



Trainees and Cardiovascular Conferences

I recently viewed a live-streamed session from the American Heart Association’s Scientific Sessions 2018 from the comfort of my own home, and I also attended (in-person) a scientific conference for a different topic within the same month. I began to think of how scientific societies engage trainees, graduate students, and post-docs at conferences. This is all from my perspective as a post-doc, so my observations should be taken with a grain of salt.

The first thing I noticed is that, in my opinion, PI’s typically outnumber trainees at conferences. This is interesting because most labs usually have one PI and several trainees. You might expect a similar parity at conferences, and I believe the reason that most conferences I’ve attended have fewer trainees is the cost of attending. I have been extremely lucky in finding travel awards to attend conferences, yet there have been several that I wanted to go to or committed myself to attend without having funding to support the trip. This can be extremely stressful and is fairly common because as a trainee, your position is not very stable.

When I was a PhD candidate in 2015, I attended a non-AHA conference. At the conference, I volunteered to be the junior representative for the graduate student/post-doc section of the society. I was elected to the position and had to return to the conference in 2016 to accept and begin my term. I was obligated to attend the conference again in 2017 as I transitioned from junior representative to senior representative and again in 2018 as the outgoing senior representative. That means I was supposed to attend the conference 3 years in a row with no clear funding path to pay for any travel. To top it all off, I graduated with my PhD in 2016, just 3 months prior to the 2017 conference date, with no justification for why my post-doc advisor should pay approximately $1,500 for my expenses to present my graduate work. At the 2018 edition of this meeting, I could finally present my post-doc work and luckily received a travel award to offset the cost of the meeting. To make a long-story simpler, 3 or 4-year conference commitments for trainees can be valuable because over that time period I met and worked with many more senior scientists, but shorter commitments would likely entice more applicants to volunteer and greatly reduce the stress involved.

One of the reasons I was elected to the volunteer position in the first place was because I was one of the only graduate students/post-docs to apply. And when I asked other trainees why they hadn’t applied, most said they would be graduating before the 3-year term finished and they didn’t know what type of lab they would end up in. An alternative option for societies is one that I recently sought out and has been surprisingly refreshing. That is the Early Career Blogger Program from the American Heart Association. To lift the veil a bit, I applied after reaching out to one of last year’s early career bloggers, Shayan Mohammadmoradi, who is now a Senior Early Career Blogger with the AHA. This is a 1-year volunteer position, and while it requires attendance at the AHA scientific sessions (I’m planning to attend in 2019), there are some incentives as an official Early Career Blogger that make it possible to attend. First, the conference registration is covered, and if you want to attend other AHA meetings throughout the year, the registration is covered for those as well. AHA also provides access to live-stream their largest annual conference, Scientific Sessions.

I study cardiovascular diseases in the context of aging, and I think supporting early career professionals is a great strategic plan for AHA or any scientific society from the perspective of aging. Early career professionals eventually become middle- then late-stage career professionals and are the next generation of PI’s. By showing that they value early career scientists, AHA will likely reap the benefit in the future.



Live Streaming AHA18 – My First Experience

The American Heart Association’s Scientific Sessions 2018 concluded this past Monday. Unfortunately I was unable to attend in-person, but I was able to catch some of the events virtually online via Scientific Sessions Live Streaming. While I have been to other scientific meetings hosted by the AHA, I have yet to attend the main event – Scientific Sessions. By live-streaming some of the sessions at the event, I was still able to hear about breaking scientific advances.

If you’ve ever felt like all of your colleagues were at a conference and you should have been there, but were prevented for whatever reason, that’s how I felt. Live-streaming some sessions at Scientific Sessions was a last-minute decision for me, but well worth it. I was able to watch Dr. Paul Ridker’s presentation at the AHA Distinguished Scientist Lecture. Not only did that provide the opportunity to hear Dr. Ridker’s update on new and exciting findings coming out of the CANTOS trial, I had never heard him speak until that moment. This was an opportunity I did not want to miss.

Another great opportunity that Live Streaming provided was the opportunity to connect in real-time with attendees who were at the Scientific Sessions in-person. As part of AHA’s Early Career Blogger team, I was able to live-tweet during the session and connect with other’s in the audience. It was a really great way to hear and feel connected to the cutting-edge science without being physically present.

This is my first blog post for the AHA Early Career Blogging team, so thanks for reading. My other posts will focus more on science in the fields of vascular biology and atherosclerosis, so if you’re interested, please stay tuned.