Features
Cell-enriched fat grafting
Cell-enriched fat grafting for cosmetic and reconstructive surgery, including breast augmentation and complex breast reconstructions, has captured the
imagination of the medical community. Dr Eric Daniels discusses the advances
Fat grafting has been reported in the literature for more than a century, with varying degrees of success. The natural question is: why isn’t fat grafting predictable? It would seem fairly straightforward, as you transplant fat from one part of the body into another.
The variability comes from a procedure where people harvest, process, and deliver differently. All this variance factored with the variance of the host leaves us with an unpredictable tool. Despite this history of unpredictability there has been a significant resurgence in lipofilling and people have begun to re-explore transplanting fat.
Rather than a simple surge of interest in an old topic, the renewed enthusiasm can be partly attributed to the discovery of stem cells in fat. Hedrick and colleagues (Zuk PA, Zhu M, Mizuno H, et al. "Multilineage Cells from Human Adipose Tissue: Implications for Cell-Based Therapies," Tissue Engineering, Vol 7, No 2, 2001) documented that one could harvest lipoaspirate from patients and isolate a single cell in which one could differentiate into lineages including muscle, fat, bone and cartilage.
Others have confirmed that adipose is not only an extremely rich source of cells that can differentiate into other cells types but also lipoaspirate contains other cell types including endothelial precursor, mature endothelial, and smooth-cell vascular cells that are crucial for building a blood supply. This population of cells has been termed adipose derived regenerative cells (ADRCs)
To isolate ADRCs, one must use an enzyme that serves as "chemical scissors" to digest lipoaspirate, liberating the cells of interest. We use a standardised, automated, and sterile method. This provides a population of cells that, in effect, contains nucleated cell matter without the mature adipocyte. Further analysis of this population demonstrates that we are isolating the stromal vascular fraction of fat, a mixed population containing endothelial precursor, mature endothelial, and smooth-cell vascular cells in addition to a population of cells that are true stem cells. This cocktail of cells likely represents multiple mechanisms of action.
If you look at the science of fat grafting, it shares characteristics with other kinds of tissue transplants. Whether it be liver or heart, transplanted tissue is subject to ischemia until neovascularisation is achieved. Autologous fat grafting should follow a pathway similar to other types of body tissue healing processes. Namely, there should be inflammation, a period of angiogenesis, as well as fibrosis and remodelling.
Nishimura and co-workers found that, in microvascular survival of free fat grafts, one observes a spurt of vessel formation early on in response to fat grafting. The driving force is soluble growth factors. (Nishimura et al; "Microvascular angiogenesis and apoptosis in the survival of free fat grafts," Laryng 110: 1333-1338, 2000.) This theme comes up repeatedly—these factors are likely the engine behind the change.
It is therefore reasonable to opine that factors that increase inflammation will likely decrease graft take and factors that increase promotion or accelerate re-vascularisation will increase graft take. Based on this hypothesis, several approaches can be attempted.
You could ask: why don’t we add platelet rich plasma? Why don’t we do vascular endothelial growth factor gene therapy? These single or combinations of growth factors are believed to, in essence, support the survival of the graft. However, this may be limiting only in the sense that you get a one-time snapshot of growth factors that aren’t able to respond to their environment. Cells, including ADRCs, are able to respond to their environment in a very dynamic way. They read their environment and can provide regulated and sustained growth factor production.
Looking specifically at the ADRCs, they are, in effect, the building blocks of fat vasculature: their job inside fat is likely to increase vasculature or draw it back as you are constantly remodelling your fat depots. In a paper we published in 2008, we initially characterised what the cell populations are derived from Cytori’s automated technology. (Lin K, Matsubara Y, Masuda Y, et al. "Characterization of adipose tissue-derived cells isolated with the Celution system," Cytotherapy (2008) vol 10, No 4, 417_426.)
From science to clinic
Of the lipoaspirate harvested from the patient, roughly half of it goes into the system to process cells for isolation; the other half is washed and prepared to mix together with the isolated cells (from the first half of lipoaspirate removed) into a cell-enriched graft. The idea is to coat that fat graft with cells that are responsive to the micro-environment, and create an interface between ischemic tissue and the graft to improve survivability.
In a pre-clinical investigation, Zhu and colleagues demonstrated that at six and nine months, one could get a doubling of the retention of volume in cell-enriched or cell-enriched treated versus non-cell-enriched. The fat was not only of greater volume but also looked better histologically. Using quantifiable methods, one confirmed a statistically significant different in volume, capillary density, and cyst formation between cell-enriched and non cell-enriched fat grafts. Fibrosis didn’t appear to change.
Other logical questions frequently posed around cell-enriched grafting are: "What do these cells actually do? How long are they there? How do I know this soft tissue isn’t going to grow for decades and be out of control?"
We have performed a series of small animal experiments that address many of these questions. In short, what we see supports the hypothesis that cell populations interact with a micro-environment of ischemia, respond appropriately and, effectively, disappear. In short, the goal is not to build breast parenchyma but to salvage ischemic tissue. In this case, ADRCs are likely salvaging grafts that are otherwise almost destined to resorb partially or entirely.
Clinical data
The Restore 1 study was investigator-led out of Japan and looked at women who had had partial mastectomies, had been radiated, and were 12 months out following radiation. The physicians were using cell-enriched grafts to restore breast volume and breast shape. (Sugimachi K, Kitamura K, Teramoto S, Mori M. "Novel Breast Reconstruction Procedure—Attempts of Breast Regeneration Using Stem Cells after Breast Cancer Mastectomy," Japanese Journal of Cosmetic Surgery vol 30, no 3, p151-160, offprint).
These particular investigators used ultrasound to measure the distance between the skin and the pectoralis major, as a 2D measurement of tissue thickness and found that, at 12 months, there was no statistically significant difference in tissue thickness between from the one-month measurement.
Cytori’s Restore 2 study—part of a post-market study conducted over the past 18 months—has completed enrolment at multiple centres throughout Europe. Interim results presented at the 32nd Annual CTRC-AACR San Antonio Breast Cancer Symposium demonstrate that cell-enriched breast reconstruction achieved a high rate of patient and physician satisfaction and improvements in overall breast deformity in lumpectomy patients. These results are based on six-month follow-up from the first 32 women enrolled and treated. The highlights from the interim data include:
• a high rate of patient satisfaction (73%) and physician satisfaction (82%) with the overall outcome after a single treatment was reported in difficult to treat breast cancer patients
• mean patient and physician satisfaction scores dramatically improved for breast symmetry, scarring and deformity from baseline to six months follow-up
• qualitative analyses of imaging data confirmed clinical improvement in both breast defect and overall breast shape
Today, more than 30 centres throughout Europe use Cytori’s cell-enriched technology for cosmetic and reconstructive surgery, including natural breast augmentation and complex breast reconstructions. The data demonstrates the addition of these cells to fat grafts produces a safe, effective and stable method of soft tissue augmentation, enabling surgeons to bring regenerative surgical solutions to their practice and their patients.
Dr Eric Daniels is senior director, Cytori, Europe/Middle East & managing director, Cytori Srl
