The Song of the Cell: An Exploration of Medicine and the New Human

Mukherjee focuses on bone, which, despite having real-world importance, has been neglected by the scientific community. The human skeleton represents one of the most complex cellular systems. Bone consists of cartilage-forming cells (called chondrocytes), bone-tissue forming cells (called osteoblasts), and bone-reabsorbing cells (called osteoclasts). A defining feature of bone is that “it grows to a point, and then knows when to stop growing” (337). This raises an important question about how cells cause an organ to grow longer.

The answer to this question lies with the growth plate, an area of tissue located at the ends of long bones in children and teenagers. The growth plate determines the length of the bone in adulthood. Studies conducted on the bones of mice by Australian postdoctoral researcher Dan Worthley in Mukherjee’s lab revealed cells located on the growth plate. These cells decreased in number as the mice matured. Dan and Mukherjee realized that they “had found that cell—the cell sitting in the growth plate, that gives rise to cartilage cells which then matures into osteoblasts—the two principal components of bone (341). They discovered a skeletal stem cell, which they named OCHRE after the different cells it makes. The gene Gremlin-1 produces the OCHRE cell.

Researchers have also found another cell type, called LR cells. These cells, which arise later in adulthood, generate and repair bone “deposited along the long shafts—not the growth plate, but the long tube of bone between the two plates” (342). The OCHRE and LR cells combined illustrate that bone has multiple sources of rejuvenation.

Mukherjee notes that every organ and cell system has its own sources of repair and regeneration. While every organ has a cell type focused on repairs, “the idiosyncrasies of repair in each organ suggest that the individual cellular Band-Aids were cobbled together and remain unique to every organ” (347). Thus, scientists must look at individual cells and organs to understand injury and repair—unless an underlying mechanism unites all repairs but simply hasn’t yet been discovered.

Cancer cells are “capable of infinite rebirth” (349) because their ability to divide has mutated. These mutations are often unique to an individual specimen of cancer, meaning that two instances of the same type of cancer will likely require different treatments and behave differently.

Mukherjee returns to the story of his friend Sam P. He recounts how Sam asked if the cancer was winning. Sam’s cancer was unusual:

It was as if each individual metastatic tumor had acquired its own program of rebirth and resistance, each battening down its own niche in his body, each behaving as if it were an independent community of colonists trapped in its own island (352).

Mukherjee told Sam that he wouldn’t know if the cancer was winning until the end. Sam then asked Mukherjee about what happens at the end. Mukherjee thought about what his other patients needed at the end and told Sam to “forgive someone. Be forgiven by someone. And tell someone he loves [them]” (353). Sam died a week later.

One of the peculiar aspects of cancer is that it shares the same “on-off” switch as stem cells, which has led some researchers to think that cancer cells have their own stem cells. Stem cells can turn cancerous, but it’s difficult to do so with mature cells. Additionally, some cancer cells appear to be able to regenerate a cancer from scratch (a characteristic of a rare type of stem cell). Research, however, doesn’t support the idea that all cancer types have stem cells.

What is known is that both stem cells and cancer cells reprogram cells in novel ways. In contrast to stem cells, however, cancer cells are selfish because they focus only on self-renewal. Researchers have tried to attack cancer cells using specific mutations or genes within the cancer, with moderate success. The big issue that still needs to be solved is why cancer metastasis survives in some parts of the body, whereas other parts (like the spleen and organ) rarely attract it.

In the penultimate chapter of The Song of the Cell, Mukherjee urges researchers to stop focusing on atomism—or examining isolated, singular units (e.g., cells, genes, or atoms)—because this atomistic worldview hinders researchers’ ability to understand the interconnectedness of cells. Mukherjee favors a holistic or comprehensive approach that appreciates the sum of all the parts of a being: “We need to know everyone who lives in this building” (366).

Mukherjee closes this chapter by summarizing the 10 tenets of cell biology. The first is that cells derive from other cells. The second is that human tissues come from cells and stem cells can produce every cell. The third is that physiological similarities are inherent in all cells. The fourth is that cells can repurpose these physiological similarities for particular functions. The fifth is that cells can communicate with each other, which leads to a system of cells. This system helps maintain key physiological functions that individual cells couldn’t do on their own. The sixth is that human physiology stems from normal cellular physiology and human pathology stems from malfunction of cells. The seventh is that a balance exists between homeostasis and pathology. The eighth is that looking at the interconnectedness of cells will help in achieving medical breakthroughs. The ninth is that humans have the capacity to build “new humans” from human cells today. Finally, many are already “new humans” due to medical breakthroughs. Nevertheless, the potential to re-engineer cells and organs even more will expand as science continues to refine the understanding of cells. This will likely incite further debate on how much re-engineering is too much and What It Means to be Human.

In the final chapter, Mukherjee raises the question, “Why not extend the building of human parts to other cellular systems?” (370). He notes that this is already being done, citing the many “new humans” he describes throughout his book. He worries, though, about what a future of trying to re-engineer humans will bring if science doesn’t stick to ethics. In particular, he cautions against mistaking augmentation (improving human features like increasing height) with “emancipation from the ravages of disease (extreme short stature, or muscle-wasting cachexia)” (373). Mukherjee favors emancipation but not augmentation. Using the story of William K., a patient with sickle-cell anemia, he shows how keeping a focus on emancipation can truly transform lives. By participating in a new cellular therapy, William K. could be cured. This cure means that he’d no longer have to live with chronic pain or the fear of opioid addiction.