This Mister Steve Ludwin is quite public about his snake adventures. The details about his method as reported in the popular press are a bit murky and so imprecise that they increase the danger for fellow travellers down this path beyond the insanely high levels it is on already.
All snake venoms are not created equal. Different species possess different levels of toxicity and different types of venoms. Neurotoxins, cytotoxins, hemotoxins, cardiotoxins are distributed in various levels and combinations with other biologically active enzymes, polypeptides and the like.
Usually that means a venom that is slowly introduced into a human system, starting at very low doses, repeated regularly and increasing the dose, gives the host a chance to adapt to this mixture of venom from one snake species.
Systematically aqcuiring this kind of immunity is indeed an ancient practice, widely employed among the Psylli and most famously by King Mithridates VI of Pontus – although for more general poisons – who lent the practice its name in modern medicine: mithridatism.
Doing this kind of prevention on his own is quite stupid:
Snake bites pose a significant, yet neglected global health problem, venom expert Dr Rachel Currier, from the London School of Hygiene and Tropical Medicine, told the Independent. But regarding Mr Friede's amateur work, she said: "Self-immunisation with snake venom is incredibly dangerous."
Detailed principles of how these counter measures devolp are researched:
Clinical Significance of Venom Antigen Levels in Patients Envenomed by the Malayan Pit Viper (Calloselasma Rhodostoma)(1986) Serial venom antigen levels were measured by enzyme-linked immunosorbent assay (ELISA) in 46 patients with systemic envenoming by the Malayan pit viper (Calloselasma rhodostoma), a major cause of snake bite in Southeast Asia. The principal effects of the venom are defibrination, hemorrhage and local tissue necrosis. Admission venom levels, which varied between 0 and 595 ng/ml, correlated with the incidence of spontaneous systemic bleeding, blood incoagulability and concentrations of plasma fibrinogen and serum fibrin degradation products. The presence or absence of nonclotting blood also correlated with the time elapsed between the bite and hospital admission. The development of nonclotting blood may be delayed by up to 72 hr after the bite even though circulating venom and raised FDP may be detected at presentation. This is probably explained by a temporary equilibrium between synthesis and consumption of fibrinogen. Venom antigenemia recurred in 12 patients (26%) suggesting continuous absorption of venom from the wound or saturation of extravascular binding sites. Admission venom levels also correlated with the extent of local swelling and the occurrence of tissue necrosis at the site of the bite. Venom was detected in 87% of wound aspirates and 88% of urine specimens taken on admission. Tourniquets, of the type used in rural Thailand, did not delay the absorption of venom into the circulation.
But serious medical research is carried out, similar to what the suspect of the claim seems to carry out, in more controlled conditions:
Production of potent polyvalent antivenom against three elapid venoms using a low dose, low volume, multi-site immunization protocol(2001) The purpose of this study was to prepare a potent polyvalent antivenom against three elapids namely, the Thai cobra (Naja kaouthia, NK), the King cobra (Ophiophagus hannah, OH) and the banded krait (Bungarus fasciatus, BF). Two groups of horses were immunized. Group 1, comprising five horses, was immunized twice with a mixture of postsynaptic neurotoxins followed by an additional six immunizations with a mixture of crude venoms of the three elapids. Group 2, comprising four horses, was immunized with a mixture of crude venoms throughout the course. For the first immunization, the immunogens were emulsified in Complete Freund's adjuvant and injected using a low dose, low volume multi-site immunization protocol previously developed in this laboratory […]
In fact, Ludwin is just using the age old technique for producing classic antivenin or antivenom. Just not in animals but in himself. The uncontrolled circumstances and his apparent wild mix of snakes involved make this not the wisest approach:
Although individuals can vary in their physiopathological response and sensitivity to animal venoms, there is no natural immunity to them in humans. Some ophiophagic animals are immune to the venoms produced by some species of venomous snakes, by the presence of antihemorrhagic and antineurotoxic factors in their blood.
It is quite possible to immunize a person directly with small and graded doses of venom rather than an animal. According to Greek history, King Mithridates did this in order to protect himself against attempts of poisoning, therefore this procedure is often called mithridatization. However, unlike a vaccination against disease which must only produce a latent immunity that can be roused in case of infection, to neutralize a sudden and large dose of venom requires maintaining a high level of circulating antibody (a hyperimmunized state), through repeated venom injections (typically every 21 days). The long-term health effects of this process have not been studied. Further, cytotoxic venom components can cause pain and scarring at the immunization site. Finally, the resistance is specific to the particular venom used; maintaining resistance to a variety of venoms requires multiple monthly venom injections. Thus, there is no practical purpose or favorable cost/benefit ratio for this, except for people like zoo handlers, researchers, and circus artists who deal closely with venomous animals. Mithridatization has been tried with success in Australia and Brazil and total immunity has been achieved even to multiple bites of extremely venomous cobras and pit vipers.
Because neurotoxic venoms must travel farther in the body to do harm and are produced in smaller quantities, it is easier to develop resistance to them than directly cytotoxic venoms (such as those of most vipers) that are injected in large quantity and do damage immediately upon injection. (also cited from Wikipedia: Antivenom)
One of the better media sources for this story has it rightly emphasised:
Lohse believes this is the first time anti-venom production is being trialed with human blood, largely because of the risks involved. And although he's grateful for Ludwin's contributions, he doesn't promote the practice.
"Under no circumstances do we encourage him," Lohse explained. "It's dangerous. It's clear that he can die from this."
Experts like Wüster, who has dedicated his career to the study of venomous snakes, remain skeptical of the process.
"I fail to see the point of it," he said. "There is a danger to it, and I'm not convinced that's where the future lies."
(CNN: Why this man injects himself with snake venom)
Source for Mithridaticum: Werner E. Gerabek Bernhard Haage, Gundolf Keil, Wolfgang Wegner (Eds): Enzyklopädie Medizingeschichte. De Gruyter: Berlin,New York, 2007, p 999–1000.